As @DisappearingGirl mentioned, there was a similar thread recently written by a Mum who was having a similar quandary after her DD came out. Here's the response I wrote to that, which got quite a few "heart" and "thumbs up" reactions, so might be helpful to you too:
Mum of a 17 year old lesbian here, so I have some lived experience and remember how tricky it was to navigate initially!
We came up with the rule that female friends could stay over, but we made her wait until she was 17 before her actual girlfriend was allowed to stay the night. When DD1 was younger, we also allowed her best friend (who is a gay male) to come over until midnight, on the agreement that I gave him a lift home rather than him sleeping here (which I am happy to do), but now they are older and both in relationships with people of the same sex as themselves, we allow him to sleep over too.
We were mindful of the fact we also have a heterosexual 15 year old DD too, and knew that whatever we decided for DD1, would have to be the same for DD2.
Teenage relationships are a minefield, I was home alone with my younger DSis for much of the time from the age of 15, and we had no rules about boys staying (or at least no one around to enforce them) and it led to some very unhealthy relationships and situations, so I wanted to do better for my girls.
Here's a link to the earlier thread, I suspect lots of the responses will feel relevant. www.mumsnet.com/talk/am_i_being_unreasonable/5250485-dds-friend-is-now-her-girlfriend-and-i-dont-know-if-rules-should-change