dont understand why you will be bringing up a baby? Why can't she? She was a woman when she had sex, so she must be a woman now and face up to her resonsibilities. same for him - why wont he be looking after the baby he made? if neither of them can or want to look after a child, then why can't it be adopted? There are still plenty of options, and time to chose. What does your daughter want? this is the most important thing in my opinion. At 15, she wont be the first or last to have sex, and no matter what sort of parent you are it can happen (unless you lock her in a room i guess)
As regards the law, if she agreed to have sex, not much can be done (see ethels post above)
has she had the std for 5 months? that would be my biggest concern - does she have any others?