Hi- it sounds like you and your friend have been through a lot. When a friend is in an abusive relationship, it can be very difficult.
You need to consider what is good for you and for your family. Having said that, though, your friend is probably pretty isolated, as most people in abusive relationships are isolated from support systems. Is there is a way that you can still be friends with her by just listening to her and being supportive? I know that you mentioned that you have tried this. One day your friend may be ready to make a real, permanent change for the better. It may take her a while to get there because of her fear (and possibly emotional and physical abuse.) When she does get ready (and hopefully that will be sooner rather than later) you can be there for her.
Remember that your friend is a victim in this situation. You don't mention what kind of abuse she is suffering, but any abuse is wrong. It is confusing, though, when a person who is supposed to love you abuses you, and that what makes breaking the cycle of abuse so difficult sometimes.
Ultimately the decision is yours whether or not to keep your friendship. I know this is not an easy answer, but situations such as these are pretty complicated.
I hope that I have helped a little. Good luck and feel free to get in touch if I can be of further assistance!