Very supportive teacher suddenly repeatedly misgendering me

So this is a pretty small thing to make a post about, I'm sorry, but hopefully some people will understand why it upset me quite a bit.

There's this teacher at my school who was the first teacher I came out to (a year ago), because she is very vocal in her support of trans people. Since then she has always called me by the right name and pronouns and essentially been ideal in that she never pressured me to think about things I wasn't ready to think about, like medical transition, and had always let me rant to her about stuff. She's my writing teacher and is always nice about trans-related things I write, and recommends me trans-related books etc. She really has given me confidence in my gender and with coming out at school, and spoken to other teachers on my behalf when I didn't want to myself. In short, she has basically been my entire support system for a year.

This weekend I was on a residential trip with her and 12 other (cis, female) students. Several times (i.e. about 25 times?) she called the group "girls". Each time I would clear my throat or something, and she didn't respond. I don't understand why she was doing this, so any insight into that would be appreciated. I was also wondering whether you think I should speak to her about it. I feel guilty doing so because she has helped me immensely in the past. But I had a very uncomfortable weekend because of all the misgendering.

Any ideas as to why this happened or whether I should do anything about it?

 

Thanks for your reply! The thing is, my school is single-sex so I am always the only boy around, and this problem has never come up before. Still, you're probably right that it's more convenient for her to call us by the majority gender. Thanks for your help

 

Yes, I think you're right actually. Thank you, that's a really helpful comment and I'm gonna go with that explanation.