Be there for her. She's probably struggling, a lot. I've been there. Let her know that you're there to help or support in any way you can. I personally think she should end the relationship as soon as possible, as it is NOT good for her. However, it's a complicated position to be in and she may feel that she can't at the moment, even if it is really tearing her apart. I waited ages before leaving, but I felt like it was the right time for me.
It depends on how close you are as to whether you feel you can share your opinion, and if you do, be sensitive about it. She's going through a tough time.
But it's great that you're concerned enough to care, so you're on the right track already, just make sure she KNOWS you care! :)
