I love the concept of tsundere being a cutesy name for a mental illness, but reading this is painful. (Especially as someone who's bipolar and autistic so I've had similar experiences. Including intense outbursts up to highschool.)
I couldn't get past the teacher acting like overwhelming her with kindness is bullying...
No, she's overstimulated. Nobody is being malicious. Just get the girl somewhere quiet and talk to her about better ways to handle her frustration. Establish a place she can go to calm down when it gets to be too much.