I can't make those kinds of decisions for her(present) or them(future). I'd be severely disappointed, and I wouldn't take part in that side of their life(I wouldn't have them bring their partner to my home, wouldn't attend any "wedding" they might have, and wouldn't advertise their orientation to anyone)*, but that's their choice, and I'd still love them and help them in whatever way they need.
* I will say that I'd probably be a bit more moveable in my position if this was my daughter and she were a lesbian, than if this was a hypothetical son. That's just a gut reaction, and not related to any religious convictions.
Let's hope you won't have more kids than the one you already have. Let's also hope than the daughter has some intelligenge, unlike her father.