<human>: My [32F] BFF and I have been friends about 14 years, but her older sister Sarah lives 1,200 miles away, so I don't see her much except for on holidays and for big events. Last year for the Christmas get-together, she brought her new partner, Casey. Now, leading up to this event, I was told this was Sarah's girlfriend. And in fact, I believe that I had seen Sarah post about her girlfriend on Facebook. BFF's whole family talked about "her" coming, so I had a pretty good reason to assume that Casey identified as female, although their appearance was somewhat more masculine.

At one point during the party, I referred to Casey as "girl," because I can't remember what it was, but I called her "girl" in the joking way you do with your girlfriends. Anyway, there seemed to be some awkwardness after I did that, and I wondered if I offended, but I let it go in the moment.

Sarah has always been bi(pan?)sexual, and is involved in the BDSM community. She has always posted heavily on Facebook about consent and alternative relationships. After this event, it seemed like she posted more about gender identity and respecting preferred pronouns. Although (hopefully!) it's unlikely these posts were directed only at me, I have been kind of worried about it since.

Anyway, this year's holiday event is coming up and I asked my BFF (Sarah's sister) about her partner's gender identity, and BFF said that she herself has always used female pronouns, but she suspected that Casey might actually be non-binary and use "they."

I've considered FB messaging Sarah and asking about her own and Casey's preferred pronouns in advance of the event, and also if they turn out to be other than female, apologizing if I offended last year. I am worried about this because I really don't know her well at all and it's kind of a personal question. I have also heard that "preferred pronoun" is no longer the accepted terminology, so I don't want to dig a deeper hole. Does anyone have advice on how to approach this?

Can you give me a shortened version of the text?
<bot>: Friend's sister's partner has non-binary appearance, and I may have used the wrong pronouns in the past. What's the best way to clarify and right the wrong if necessary?