These kinds of things are normally learned from the parents. There is a good possibility her mother was with a man much like the man that she is with.
There could also be some insecurities that she is facing but from the sound of her, that's not her only problem if it is a problem at all.
My guess is that she is dealing with this man because her mother dealt with a man similar. After seeing something for so long, it kind of becomes embedded in you. I am much like this woman because of the way my mother was and I see that, but it is still not any easy thing to change.
I hope your friend can learn that she deserves better and that there is better out there. I wish you and her well! TC!