Well, then you just have to tell yourself it isn't your fault and it never will be. The only person to blame in that situation is the asshole that is twisting her mind the way he is.
Sadly, most of the girls in bad relationships are very smart. I don't care what all the psychologists say, it isn't all about daddy issues and so on and so forth. Even though I'm adopted, I grew up with a great dad. And if he had known what was going on when I was in that relationship he would killed my ex and probably would today if he ran into him. But, as I've said. Those guys known how to get into a girls head. Once someone knows your fears and insecurities, and also physically intimidates you, you stop being yourself and you become who you have to be just to live from one day to the next.
It's hard to explain. But, its like living in a fog. Time passes and things happen, people try to help, but it never really reaches you. The only thing that gets through is when he starts to get mad and you try to make him happy. But, that never really works for long and you go into an even deeper fog to block out whats happening. You deny it so much you really believe nothing is unusual or wrong. Then when you do realize its not normal and wrong, you start to think maybe you deserve it. That you're a bad person or whatever term he uses to make you feel bad and he 'doesn't want to do it', but 'you make him so crazy'.
In the end the only person that can wake up from the nightmare is the girl. No one can make her wake up... I think maybe thats why some girls go back into those sorts of relationships... They just have to wake up themselves.