Something to think about, take it or leave it. My parenting style won't suit everyone, but we chose to trust our children and their opposite gender friends.

My 16yo son's best friend is a girl he's known since they were 4 and we've always allowed sleepovers. We limited them to the lounge room from about 10yrs of age and her parents have the same rule at theirs.

It turned out that she's gay, so it wasn't ever an issue. But the thing is that even if she wasn't, what's to say that they'd ever like each other that way?

Just because someone of the opposite gender is technically available, doesn't mean we're going to automatically be attracted to them.

Maybe ask your daughter's friends' parents how they want to handle sleepovers going forward would be helpful, too.