Hugs. I’m pro-life. I’m from a Catholic family, but I’d estimate that three fourths of my cousins’ kids are no longer practicing Catholics. However, a surprising number of them just couldn’t go through with an abortion when they or a GF became pregnant in less than optimal circumstances. (Yes, I know I don’t know about those who did.)
I’d estimate that in about 80% of those cases, the baby was the best thing that ever happened to the mother and/or father–even though nobody thought so at the time. I have extended family members who really got their acts together BECAUSE of the baby.
That said do NOT push marriage; that is a separate decision. It is important to have the dad sign the birth certificate when the child is born. (Social workers arrange this in many, if not all,US hospitals.) That simplifies child support if the couple does split up.
I respectfully disagree with @oldfort I know that OP’s daughter has had mental health issues, but IMO this approach–discussing all these questions with them-- infanticizes the couple. This is their problem and the mind set OP should create is that she can’t be counted on for any help at all; the couple has to figure it out for themselves.