I've been sitting on this for over a year, whew!
This story sticks to the canon comic with a slight divergence.
So Sunset wasn’t attacked, assaulted, or tortured, her friends don’t want her dead or beaten, and the revealed (known) secrets are: an embarrassing nickname, silly photos from a sleepover, and a bad grade. This isn’t life or death stuff, it’s juvenile high school bullying. It helps to keep that in mind for this story.

Go to hell where you belong, DEMON!

Sunset stared at her locker that morning, at all the many written words covering it, and sighed. It was the last day before winter break, and she wasn’t sure if she could handle even those few hours.

Get out of our school!!!
How do you live with yourself??
Demon bitch, I hope you get hit by a car

They were written with pen and pencil and blood-red marker, on full sheets of paper or ripped corners of lined paper. Even some words scribbled right on the cold gray metal.

Do us all a favor and just disappear!

She began to have trouble reading them, her hands were shaking and unshed tears blurred the jagged letters. Was she really so hated? Did no one believe her? She thought she had finally been making progress, making friends.

Monster, in black sharpie.

I knew you couldn’t be trusted, in tight little letters.

Somehow, she thought she had been forgiven.

“Maybe she’ll finally take the hint,” someone murmured behind her. She spun around but she didn’t know which of the students had said it, as they either glared outright or ignored her completely.

No one wanted her here.

A shove came from behind, knocking her to the floor and making the book—her journal—spill to the floor. The world around her that had seemed so loud and overwhelming, suddenly grew quiet as her eyes fell on Twilight’s last words written to her.

“Sometimes all you can do is stay strong. Remember who you are. And Find your family.”

Maybe that was the answer.

…just disappear…

All she had to do was disappear, and everyone would be happier. She wouldn’t have to bear their stares or their hatred anymore. Perhaps this was something she should have done a long time ago, if she hadn’t been such a coward. If she hadn’t been so foolish to think any of it was real.

As if she could have ever been truly forgiven.

During the mid-morning break she took her chance, slipping away through the crowds as she snuck into the empty music room. She pulled out her journal, and idly flipped through the pages thinking of the memories of it, her last tie to Equestria. In her last class she had written a note to Twilight saying goodbye, and wrote a separate one for her friends that she had placed in the front, one corner sticking out so they’d find it. Twilight was their friend more than her; it seemed right that they should keep it.

She tried Applejack’s locker, then Rarity and Fluttershy’s, then the rest. All of them were locked. Rainbow’s locker gave a clatter as Sunset banged her head against it- just her luck. She had hoped at least one would be unlocked, heck, she was pretty sure Pinkie Pie’s was empty, anyway. But they were probably more cautious with what was going on.

She began shaking the lock on one of them.

“Ugh, come on, you stupid—“

“Um, Sunset?” a small voice called.

Sunset jumped, turning around to seeing three young girls huddled by the doorway- Applebloom, Sweetie Belle and Scootaloo. She looked at the locker she had just been abusing before dropping her hands.

“This isn’t what it looks like,” she said, dropping her shoulders. Great, just great.

“What were you doing?” Scootaloo asked, before getting elbowed by Applebloom.

“Actually, we wanted to talk to ya,” Applebloom said, toeing the ground and looking nervous. “You, uh, haven’t figured out who’s behind the Anon-A-Miss account yet, have ya?”

“Wait, you don’t think I did it?” Sunset said, stunned. “Wow, you must be the only ones in the whole school.”

“Well, that’s because…” Sweetie trailed off, twisting her fingers nervously.

“We know who really did it,” Scootaloo said.

“What? Really? Who?” she asked quickly, stepping closer to them. Hope flared hot and bright in her chest. If she could prove who did it, maybe she could clear her name. Turn in whatever bastards did this to her. Get her friends back…

“Yeah, the real Anon-A-Miss… is us,” Applebloom said.

Sunset stared as if it was some cruel joke, but none of them were laughing. None would meet her eyes. They looked… guilty.

“No. No, that doesn’t make any sense. Why would you… wait.” She looked more carefully at them as the pieces came together.

Pointing to Applebloom, she said, “You were the one who told me Applejack’s nickname, over the phone. And Sweetie Belle, you were at the slumber party that night. You… you got those pictures off my phone somehow, didn’t you?”

Sweetie Belle nodded, looking to the floor.

“Scootaloo?” Sunset prompted.

“The varsity soccer team practices before we do, so when no one was looking I took pictures of some of Rainbow Dash’s papers,” she mumbled, staring hard at her feet.

Sunset leaned back, the lockers giving a faint clatter as she stared at them in the growing silence. Of course. She hadn’t even thought of them, but they were the only ones who it could have possibly been. How had she let herself be so blind? Except… it still didn’t make any sense.

“Why would you do that? To your own sisters?” Sunset said, clenching her hands into fists as that flicker of hope turned to fury. “What on earth were you thinking?! Do you have any idea how much they’ve suffered? How much everyone’s been hurt because of that damn account!”

They flinched, Sweetie grabbing Applebloom’s arm as if Sunset might strike them.

“We didn’t want to hurt them. Not really,” Applebloom said, struggling to not shrink back.

Scootaloo gave a little cough and glared at her.

“Yeah all right, maybe a bit,” Applebloom admitted, frowning. “We, or, I mean, well... I was jealous.”

“Jealous? Jealous of what?” Sunset repeated, only growing more confused. What could she be possibly jealous of?

“Well, Applejack was always spending time with you and her other friends, way more than they ever used to. She doesn’t ever have time for family anymore.”

“Same with Rarity,” Sweetie Belle squeaked, still half-hidden behind Applebloom. “We barely even talk anymore. She’s always doing stuff with the band now.”

“But that wasn’t the main reason. Not really,” Scootaloo said.

“Then what?”

“We wanted to hurt you,” Applebloom said quietly.

A chill ran through her, quite apart from the winter cold outside.

“Me. You did all this… to hurt me.”

“We didn’t mean for all this,” Sweetie said, tears in her eyes. “We just wanted to, I don’t know, to make you feel bad. Give you a taste of your own medicine after how much you hurt our sisters—hurt everyone! You were a bully for years. We know they forgave you, but they weren’t friends for so long because you drove them apart! I kept having to hear Rarity cry at night because of things you did.”

Sunset opened her mouth—whether to argue or to make some snippy comment about Rarity crying, she wasn’t sure—but she closed it again. It was true. She had hurt them.

“Fine,” she said, the words thick in her throat. “You’re right. I hurt them, so maybe I did deserve—“

“No!” All three girls said at once, looking appalled.

“We weren’t… we didn’t mean...”

“It wasn’t supposed to be like this,” Applebloom said, taking over from Sweetie Belle who was trembling. “It was fun at first, everyone thought it was hilarious. But then…”

“We didn’t think it’d get so out of hand,” Scootaloo continued. “We were going to stop after a few days but everyone seemed to like it, asking us to post more.”

“Then they started sending in other secrets, and everyone was so excited… we got carried away. It… it wasn’t supposed to be this bad,” Applebloom said, and the three girls lapsed into silence, heads bowed.

“I don’t understand, though. Why are you telling me this?” Sunset Shimmer managed to say, her fury chilling into numbness. Did they know no one would believe Sunset? Did they think they were safe? Except this wasn’t gloating—it was a confession.

“We’re tired of all these lies and secrets, of making everyone miserable. After today we’re shutting down the account. And…“ Applebloom took a deep breath. “And we’re gonna tell everyone the truth.”

“It’s been getting really out of hand,” Scootaloo said, her voice much quieter than usual. “At the beginning it was all dumb stuff: funny pictures or little jokes. We didn’t think it was all that mean.”

“I still think piggly wiggly is funny,” Applebloom muttered with a pout, before Sweetie Belle slapped her arm.

Scootaloo went on. “Then people started sending in other stuff, and people thought it was pretty funny too. And then they started sending worse stuff and it became a lot less funny. I mean, really bad secrets.”

“We didn’t post them!” Sweetie said quickly. “Not all of them, and none of the really bad ones. Just ones we thought people might find funny, or it was a secret that someone was hiding. We weren’t trying to hurt people.”

“But then some of them started getting mean and messaging us all the time,” Scootaloo said. “Then they started threatening us when we wouldn’t post their secrets.”

“An’ now someone keeps tryin’ to guess our password and hack the account. They haven’t yet, but if they get in and start posting those other secrets…”

“It’ll be bad,” Sweetie Belle said in a low voice, a haunted look on her face.

“We’re gonna stop it. And we’re gonna tell everyone it was us. They’ll have to leave you alone then.”

“We saw your locker this morning,” Scootaloo said after Sunset didn't reply. She wasn't sure how to reply.

“That was awful,” Sweetie Belle whispered.

“Ah’m sorry Sunset.” Applebloom stepped forward, raising her chin and trying not to flinch. “And if you gotta be mad at someone, it’s me. I’m the one who started it. I got jealous of how my sister was hanging out so much with you, and I was the one who made the account.”

“I’m sorry, too,” Sweetie said, also stepping forward.

“Me too. This whole thing was pretty messed up,” Scootaloo said.

Sunset looked away from the girls; she needed to think. The answer was easy: let the girls spill the truth and shut down the account. There. Done. All laid out on a silver platter. The school would realize she was innocent. Her friends would talk to her again, things would go back to normal.

So why did she feel sick? Why did she hesitate?

Her gaze fell to the journal. With numb hands she picked it up and flicked to where she had last written, a farewell note to Twilight: thank you, sorry, I'll miss you...

There on the opposite page was Twilight’s words from last night, and it was these she sought out.

Sometimes all you can do is stay strong,
Stay yourself,
And find your family.

Her family, her friends… she would never be able to find it if she stayed there, and no one would ever trust her, no matter what she did. There wasn’t anything left for her there.

“It’ll be all right,” she said softly, more to herself, before turning and holding out the journal. “Just… do me a favor, ok? Just give this to my frie... to your sisters. Wait until after school.”

Applebloom reached out like she was being offered a tarantula. “What is it?”

“Doesn’t matter. Just give it to them once school is over. They’ll know what it is.”

“What about us? Aren’t you mad?” Scootaloo asked, as the two other girls squinted at the hardcover book. “After everything we did? Aren’t you going, I don’t know, shout at us or something?”

“Nah." Sunset shrugged. "I already made my decision. It’ll be fine. You said you’re going to shut down the account today?”

“Yeah, right after school,” Sweetie Belle said, looking unnerved by Sunset’s relaxed response. “We already made the final post saying it was us.”

“Don’t bother,” Sunset said with a wave of her hand, surprised at herself but too numb to care. “As long as you stop it, and stop spreading rumors, I don’t mind. We’ll keep it between us, how about that? Someday you should tell your families, at least your big sisters, but for now let sleeping dogs lie, I think the saying goes.”

“Wait, what?” Applebloom yelped, while the others gaped at her. “But then everyone’s going to keep thinking it was you!”

“By this afternoon it won’t matter. By then I’ll be far away- it won’t hurt me anymore.”

“Far away?” Scootaloo said, looking uneasy. “Why? Are you going somewhere?”

“Don’t worry about it. And...” Sunset took a deep breath, closing her eyes for a moment. “Look, I’m sorry to you three as well. I don’t think I ever went after you directly, but I know my actions hurt a lot of people. I know I hurt your sisters. I understand if you’re still mad.”

She bent over and picked up her backpack, ignoring the shocked faces of the girls. Maybe some things can’t be forgiven, she thought. But if anyone knew what it felt like to be forgiven, it was her. She turned around to grab her backpack and felt a hand grip her sleeve, holding her back.

“Sunset, I…” Applebloom said in a small voice, still clutching her sleeve, “I really am sorry. Honest. You don’t gotta do this.”

“Don’t worry about me. Take care of your sisters, okay?”

The warning bell rang, and she calmly walked to the door, having no intention of sitting through another class ever again at that school.

“Sunset?” Sweetie Belle asked in a quavering voice, making her pause. “Are you going to be all right?”

Sunset Shimmer gave a short nod, a hint of a smile, and then she closed the door, leaving behind three miserable, terrified girls.