F.X.
I don't understand your last sentence.... is she saying for YOU to take the baby and she is leaving, or that SHE is taking the baby with her?
If she wants to leave the baby, you have a lot of legal issues to deal with.
If she wants to take the baby and leave, I wonder if there is really anything you can do. As long as there is someone out there willing to take her in and support her financially, she has no reason to come home to you. I went through the exact same thing when I was 18 (went to live with other relatives and wanted nothing to do with my parents) but I didn't have a baby. But after just a few months, I was able to get the partying out of my system and decided to come back home and go back to school. She has to face up to being a parent and the responsibilities that go with it.