If you did not want you or her to be looked down on for having premarital sex, you should not have had premarital sex. And now you’re looking at possibly disposing of your baby, to take away its right to live, to cover up what you did (even though God sees anyways). Does that sound right to you?
Premarital sex and abortion are both grave matter. You should not have done the former, and you should not do the latter.
If she is truly contrite, she will be forgiven, but that also means turning away from the sin, trying not to do it again. That means no more premarital sex. If she continues doing it, she is not truly contrite. Keep the baby. Her parents should forgive her, because that is the Catholic way to go about it, but I can’t promise that’s what will happen. They are only human, after all. Humans mess up.
But whatever you do, don’t take the life of your baby. That would be cruel and unjust to the baby, and both you and your girlfriend will have mental scars from it. Not only that, but it would be a mortal sin.
Own up to what you did. Face the consequences of your actions. This goes for her, too. Do the crime, do the time. Do not punish the baby by taking its life away when you and your girlfriend are the ones who brought that baby into existence in the first place by choosing to have sex.
If I sound harsh, I don’t mean to. Abortion is one of those things that enrage me even just thinking about it.