Please help? I don't know what to do about this?

My friend Haley and I have known each other for five years, and she has always been really happy-go-lucky. Recently she started getting really dark, doing drugs, drinking, and cutting herself really badly.I try to get her to talk with me but she won't. now she wants to move in with her alcoholic mother, and run away when she is 18. she was supposed to leave in June, but she told be today that she told her mom something- she wont tell me what it was- so her mom is coming to get her next month. I'm so worried about her, and I don't know how to help her. She has literally been my only friend for the past five years and now she is leaving, and she is hurting, and I don't know how to help her. Haley has an Iron will, and a smart mouth, and she is being really flippant. I know something is wrong, and it's plenty easy to jump to conclusions, but I was hoping you would know how to hlp her.