After Tirek was defeat, Eris was considered an accomplice. Because of this she was sent to Canterlot dungeon and waited for being judged for her crimes. But something made them consider to give her a little chance, all of them except one.

Offtopic:
This is a new book series that I'm making, basically changes the gender of the characters.
This is the link(to my blog post) in case you want to know how they gonna be called. Have fun.