iam1butterfly is correct, there isn't much you can do. She will have to make that choice on her own, even if you don't like him. My best friend is with someone who is equally abusive mentally and verbally. They have separated but it took 3 years for her to finally kick him out, she still doesn't file for divorce yet when I think she should. But she will have to do it when she is ready. Same as your friend. In time she will get the strength to leave him, you just have to be her shoulder to cry on, not judge her for her mistakes and support her through it all. Even though it is frustrating, you would only hope she would do it for you if ever the time should come that you are in a bad situation. Good luck.
Aside from being a compassionate and supportive friend, there's not a whole lot that you can do. Your friend is the only one who can break free from this cycle of abuse.