I feel te cat thing is a little overboard now. And makes me think that if the school was so harsh the students that put a F#ing death cat in a locker are just as crazy as this girl is now.
But in reality, this felt like a cheap way to try to make the reader emphasize with the antagonist (yes I'm taking her as the antagonist).
With this kind of backstory I fear for the life of the MC, he may end up in a grave.