Not being a parent, and not likely to be ...
Take this with a grain of salt. :-)
It's good to have convictions about things. But I don't understand how you can have such strong views about this when there have to be other circumstances which haven't been discussed.
I understand that this is hypothetical.
Was she "going steady" with someone? Was it a one-night stand? How long had they been dating? Do they love each other or was it hormones?
How good is she in making reasonable decisions? Did she intentionally get pregnant to spite you? Was this completely out of character for her? Is she sneaking around without your knowledge or were you inattentive to what she was doing?
I think the circumstances matter a great deal.
I knew a couple in high school (late '70s). They'd been dating for several years and fooled around a lot. She got pregnant when she was 16 or so. (His father was a minister.) They got married, earlier than they planned, and she had the child. They had a few more too. They were a wonderful couple and were having a great life together the last I saw them. He had his own business and was doing pretty well.
I knew another girl in high school who got pregnant and had her child and continued to attend high school and I think went off to college. Abortion wasn't an option for her, and she had no interest in marrying the guy. I think her family helped raise the kid. She was in the honor society.
I agree with you that it's most likely that a girl having a child at 16 is going to have many difficulties in life. It'll be hard on you and her no matter which way the decision is made. But I don't think you can declare at this point that "this is the way it's going to be" without considering the circumstances.
And I agree with Simon that if she's in this situation it's very difficult to impose your will at this late date.
In short, I think your reaction should depend on the circumstances. It may be that imposing your will on her (by causing her to feel rejection, or maybe causing her to feel grief over the loss, etc.) may be more damaging than her having the child. Having her live on the street, or in a crack house or something isn't something anyone should be forced to do - but some people feel they have no choice.
My $0.02.
Cheers,
Scott.
