Hello my sis,
Raising children brings a whole new meaning to the broken heart. The pain in watching my three daughters struggling with their own confusion is a hurt that will not be forgotten.
The worst thing to do is to pretend. And also realize that grace does not teach us that we are supposed to be accepting of perverse behavior, but that this is what we have been delivered out of. In Christ, All of it has been condemned equally. Christ's death and resurrection did not make it OK, He put it to death and has raised US to new life.
Consider, your daughter already KNOWS that you do not approve of lesbianism. Regardless how she came across to you it was probably very difficult for her to finally "come out". Don't be afraid to let her know how you feel and what you are going through because of this. She will either pick up on it from what you don't say and/or in watching your reactions ... or you can talk to her like a real person.
She knows you better than you can even imagine, but I would think that she has been hung up on viewing mom "after the flesh" just as we viewed Christ after the flesh. For her to know that you are broken-hearted over this choice of hers but that you really do love HER is a treasure of grace that cannot help but impact her in ways that you or I could not even imagine.
If she comes over to your house with her friend, it would be more honest to be right up front with your daughter and ask that they restrain themselves while staying over than to pretend not to notice only to let it all build up and keep any real communication from happening. Remember, they really do know.
We have been freed in Christ to truly be alive. That includes the experiencing of the broken-heart, for it is a gift of God to us as through the pain we experience the suffering of Jesus himself.