Discord's been reformed, or so we've all been told. Sure he's as unrepentant in his mischievous ways as before, but who are we to argue? So, when he tells Princess Celestia that he wants to reach out to his fellow former villains, how can she say no?
Why not humor the very embodiment of Chaos, if he wants to do something constructive with his time? The fact that Princess Celestia knows a couple of individuals that could actually use some support in dealing with their past actions, doesn't hurt either. Discord might not be the ideal candidate for the role, but how badly could it turn out...?
...It's probably best, that Princess Celestia plans on keeping an eye on things anyway.
--A fun one-shot, that lets me set up the groundwork for some future stories.--