I had a difficult time at that age myself. I ended up being kicked out at 17 and it was such a good thing for me. I worked full time, finished high school, found my first place and launched my life without my parents abusive crap.

I'm not saying she she move out. I'm saying she isnt helpless in this situation if it is really detrimental for her. Another thought is that she is less than 2 years from 18. She could stick it out, finish high school and then bounce.

All you should be doing is supporting her decisions, whatever they may be.