I NEED HELP WITH THIS DEPRESSION!?

My bestfriend is 15 years old and is going through depression at the moment. Her parents are alcoholics and get drunk almost every night now. They were abusive to each other when she was about 10, but now its all verbal abuse towards her and each other. Her parents blame their relationship problems on her claiming that she doesn't let them be close towards each other. The mom gets drunk and yells, and says you have a great life you shouldn't be depressed and calls her names and puts curses on her saying she hopes she has a daughter as bad as her. Her father cheated on her mother when she was about 9 or 10 and she was the one who caught it, she saw her dad with another woman, therefore she doesn't trust her father anymore because he tricked her. The parents were separated for 2 years and she hardly saw her mom during that time period, the mom used to say things like, your going to have a new family now, and would get drunk a lot. Saw father on the weekend, he would pass out a lot and she would have to take care of him. But now she doesn't want to be nice with her parents anymore, she doesn't want to fix the relationship she has with them because she knows they wont stop drinking and being mean to her a lot. She has someone very close to talk to when she's down who she calls "Her mom, away from home" She has cut herself once about 2 weeks ago, but says she will never do it again. She has lost 5-6 lbs this month and is having trouble concentrating in school, she's restless, sleeps a very long time on the weekends, she self loathes, she gets nautious in her stomach, she has extreme sensitivity to criticism and she feels guilty when she says something she shouldn't of, and has lots of regrets. A lot of time now she just wants attention because she doesn't get a lot, she feels her life is coming to nothing! PLEASE HELP comment below <3