I think any sort of confrontation you make on her behalf will only make things worse for her at home. I suggest you be a source of support for her, and suggest that if things are too bad, she can talk to a counselor at school or ask a relative to let her move in with them.
Giga's right, BTW. The things you mentioned, while certainly unpleasant, are minor compared to what she might experience in a foster home. Sometimes you have to pick your battles.
Relax... I'll need some information first. Just the basic facts - can you show me where it hurts?