G.B.
Can she get someone else (family friend she likes, minister she knows, former teacher/coach she admires, etc.) to talk to her daughter or do an intervention with the whole family? Might she be pregnant? Can she talk to the mother of this BF? Can she talk to the 2 of them together? What she doesn't want to do is corner this girl and make her feel even more defensive. Sounds like this will end badly but she may grow up out of this if mom can't stop it. She should try hard to maintain communication with her through this period, being very supportive and stating her unconditional love no matter what may come. This girl thinks she's running toward this kind of love so she needs to be reminded that she can find this at home. Presenting a compromise might be useful, like dropping out of college & moving home on a more adult basis than she had before, maybe getting a job & buying a car etc. Trying to postpone her moving away for 6 mos or a year & see if she'll agree to that.