Maybe she is lonely, often young girls have babies because of this. I know you said she has friends, but maybe she feels she doesn't actually connect with them. It is possible to be lonely surrounded by friends.
Also maybe she doesn't see much in her future, or may be overwhelmed by the enormity of it all, all the choices and decisions open to her.
I would talk to her about it. It can be hard, but once you start talking it will get easier. As long as you don't say her way of thinking is wrong (or her friends are wrong, even if you think they are, she would have to make that decision on her own) I'm sure she'd talk to you. She might even be glad to discuss these issues.