What to do about a horrible horrible person...?

I'm with dead dolly on this. You can either take some cles and learn how to fight and block effectively or you can turn her into the principal/counselor. But I know the second option is pretty much not going to happen because she will get more pissed off and probably come after you. Being another non violent person (only violent when needed), have you friend teach you to fight better if you can't take the lessons to fight proper. Taking self defense martial arts is actually worth the money that your mother would spend on it. Not only can it take care of school bullies but it can prove useful later in life also.