I think I have the solution
What you do is, get a time machine, go back in time as many years as she is old, and then leave her there in the past. Go back to the future (ie the present) and then you don't have to worry about it.
The downside is, if she has a girl, it's pretty likely that the daughter she had grew up into your girlfriend, so you basically knocked up your own child. Plus, there's the whole "she gave birth to herself" thing
And of course, if she gave birth to a son, then chances are good she's really your mom, and you are your own father.
Kinda messed up either way, but at least you don't have to worry about raising a kid.