I would do the same thing I would if she were my best friend- and more. I don't have a daughter yet, and my sons are too young to even try to conceptualize them as grown, sexual beings.... my oldest is 3 1/2.... but I would help her in every way I could, and be a loving, involved grandma.
School shouldn't be an issue, since my children will either be unschooled, or attend the charter school I want to start. So either way, she would have no problem finishing school, and could bring the baby. I would be able to help her with childcare while she attended college and/or worked, and ideally she would just build a small house on my property.
Or if she didn't want to keep the baby, then I would support her too. If she wanted an abortion I would teach her gentle techniques (starting with simply asking the baby to leave) I would support her in every way possible, and help her to have a peaceful pregnancy and birth, ideally.
If my sons were responsible for a pregnancy at that age, I would support the mother, if her family was unsupportive, and treat her as my own child. I also would not stand for my son not supporting his baby. (at the very least) If he decided to anyway though, I would not try to force him, if his supportive is not coming from a positive source, then she's better getting it from positive ones, I'd offer her that alternative.