17 yo daughter wants to come back home and bring 18 yo bf ...?

My stepdaughter went to live with her mom @ 6 mos ago. My husband and his ex have joint custody, husband is primary. Therefore, ex was not able to enroll her in school in her state. (dad cant enroll her there because he has no proof of residence.) So once daughter left, she had to quit school. She has said all along that she wants to finish, and now she has finally asked to come back home. BUT-- she has also asked if her 18yo bf can come home with her. He seems ok, has a job and is going to start college next semester. She says they have talked about it and he is willing to help with the bills, and daughter has always helped us with the younger kids at home and helped us with the household chores- laundry, dishes, keeping things picked up, etc. I'm torn between both sides of the issue. If she will finish school, then maybe ok. But I'm also afraid of the drama from every angle imaginable that will no doubt come along with the situation. So... any ideas?