Don't walk on eggshells, that's no way to live - I should know - I did it with my first husband for many years, in the end it took a massive mental health crisis to make me leave.  I think it's fine to wonder if a young teen is settled in their sexuality or if it's a phase - my SD23 "came out" as bisexual when she was about 14, but has never had a girlfriend and I think it's all forgotten now - she has had a number of boyfriends. 

Your SD is just trying to put you in the wrong - teenage girls are difficult at the best of times.  Try and disengage a bit, keep your own counsel,  and don't allow her to push your buttons - being able to do this is putting her in a position of power over you.  

Well the damage has been done and your SD is going to feed off her "victim" story until another person "victimizes" her and lets you off the hook. Best you can do at this point is ignore ignore ignore. My BD claims she's bi/trans/no-binary...it just depends on what day of the week it is. I've learned to just go "Hmmm that's nice." and move on I don't feed into it because for some reason teenagers today all need to feel like they are a super special sparkly unicorn above all others.

OSD "came out" as bisexual about two years ago (age 14 or 15?). We were like, "Meh." I'm sure she expected drama. We all met for dinner one night at a restaurant with BM. I did NOT want to go at all, but whatever. It was supposed to first be AT BM's home, uhm never, ever there so I agreed to a restaurant since I was specifically invited. OSD hardly spoke to us except for snarky remarks and her coming out announcement. Then she hailed BM for the bill and she almost RAN to BM's car, not a single thank you or goodbye.  DH was PO'd. I was not surprised. I said that I didn't care WHO she slept with, but as long as she's a b*tch and is rude to people - THAT is my judgement of her.

Shortly after DH took OSD with us on a vacation. She was allll about gay rights and how horrible heterosexuals were and so on. She was trying to show off for her aunt I'm sure. And show how progressive she is. Well, we're all ultra-liberal and her arguments went no where because she was trying to create false pretenses. And then she decided to criticise how one of my best friends on this planet came out. Oh, I turned to her and said, icily "You do NOT have any right to comment on my friends or their experience that you know NOTHING about." I think that's one of the last things I said to her on that trip.

Anyway, I hold firm that a b*tch is a b*tch no matter who she sleeps with.