Contrary to popular belief, getting pregnant does not emancipate a teenager other than medically. If she is under 18, then yes, her parents can absolutely tell her where she lives. If she refuses to come home of her own accord, they can come and get her, or send the police to get her. And if the people she is staying with know that they want her to come home, and they do not send her home, they can end up in jail.

So if she is not living with her parents because they are okay with her living somewhere else, that's fine. But if she is living with someone else in defiance of their wishes (perhaps her boyfriend's parents? Hmm?) they they had better tell her to get her pregnant little ass back where it belongs, because Mom and Dad have 100% say over where she lives until she turns 18.

And if Mom and Dad previously gave her permission to live elsewhere but now have changed their minds and want her home? She goes home. They can retract permission at any time. Repeat for those following along at home - the ONLY ones who have ANY say over where she lives are Mom and Dad. As long as she is even one minute under 18. Pregnant or not.