Essentially, in any case like this, you need to think of what your objection would be. For a lot of parents, they don’t like the idea M/F sleepovers because they’re worried about the teens maturity levels and might end up pregnant (or possibly with an STI although that’s probably less likely the younger you are.) Do you just have a blanket objection to unmarried sex? To the idea that your child may be sexually active at this age? How do you define “sexually active?” Because if they’re lesbians, they’re not having PIV sex. For me, this would be a no brainer. Sure. If they are messing around, they’re already doing it somewhere and there’s no chance of pregnancy. But if your objection is just that you don’t believe in unmarried sex, while I don’t personally think that’s a great idea, if you’d hold a heterosexual child to that standard, you shouldn’t really have a double standard for a gay kid. What if your straight kid wanted a sleepover with someone and you weren’t sure if they were in a relationship or just friends?
Some kids might not come out to supportive parents. My kid didn’t for several years, even knowing that both my husband and I were very LGBTQIA+ friendly. They just weren’t ready. It has nothing to do with us.