What do I do about this situtation?

My girlfriend has a daughter who is 19 years of age. I have a roomate who is 28 years of age. The two of them started seeing each other against my wishes. Well guess what, she is pregant! She is dead set on keeping it. Apperently it takes two to tanjo but, the decision to keep the child is only hers? I think that she is going to ruin her life at 19. He does not want the child either.