The creepy scumbag teacher gets no sympathy from me, I hope that's the last we see of his abusive ass. He doesn't even have to die, he just needs to permanently disappear from that school. Too bad for him his target isn't some pushover, and he's the one who got pushed. Literally.
She might be going crazy, but at least this act of impulsive violence is a net benefit to the students at school, including herself. He had it coming to him.