Friend in an emotionally abusive relationship?

I have been in your situation. All you can really do is express your concern to her. Sounds like he is quite controlling. There is only so much you can do or say. She may take you advice to a certain extent but she has to realize its not a healthy situation on her own. Don't push the situation too hard, you may lose a friend. But like i said just express your worries to her as much as possible without upsetting her, let her know that it is only because you care. Also let her know that her friends will be there forever..the boyfriends may not.