One bad day is not a valid reason to destroy a city. Not even if you are an alicorn. At least, this is what the law says. It is not what the law used to say back when Celestia ruled alone and the town south of Canterlot still existed. No one remembers what the town was called, because Celestia burned the records too that day. This means Twilight is stuck having to take her frustration out in other ways.