how sad. I'm sorry to read this an unsure if I could give you any advice. I agree its not friends place to say to leave someone. Perhaps one day when she is begging and tearing for an answer: ask her to think on but don't answer, if she is truly happy and should be treated the way he does, is it really deserved.... perhaps that can help her realize something in her self. It may be tough love but perhaps it will help her realize you can't give her answers, she has to do what is best for her.

I am sorry if that is no help. You are a great friend to be doing what your doing. I hope she finds strength in herself to realize she is great and does not need a man like that.