How do you feel about the boyfriend?
Having been in a controlling, abusive relationship, that's what this could be. (Not to throw another possibility out there!)
Women in controlling relationships often times are desperate to stay because they are so paranoid about what will happen if they leave/separate. I know my exhusband appeared to be "the nicest guy" to anybody on the outside, but over time just wore me down to feeling like nothing.
Good luck MadKarma, I hope you get to the bottom of the issue with your daughter.