First of all only have sons, however if I did have daughters yes she would carry the baby to birth and then my wife and I would raise the baby. At 18 she could decide then what to do either allow us to continue raising the child or she could. I am sorry but you cannot blame the baby for this. The Neanderthal is to blame.
Easy to SAY - but like I said, until and unless you have actually faced it = you cannot rightfully judge. (I notice, in your pontification, that you would not give you young daughter any say in whether or not to carry the pregnancy thru'. - Also, after she has carried it thru', and you have raised it in your home for several years = then she would get to choose whether to let you continue as it's parents or she could take over = at 18 - to raise a child already a toddler. I assume you would continue to assume the financial support of the two, and not plunge her and the child into the bleak outlook of a single mom with only a high school diploma?
Come back and tell us how things went AFTER you have had to actually face the situation.
For me, in this situation and many others, I try to remember; "There but for the Grace of God, go I."