Not quite an experience of "children changing their label", but from an adult who's been through something similar:
My first label was "straight". That's what I would've told you I was if you'd asked me when I was your daughter's age. I didn't figure out that I liked girls too until I was 18—partly due to growing up in an environment where LGBT+ people were either not mentioned at all or else openly disparaged (so, on behalf of all the non-straight kids who had a similar experience, thank you for being a safe & supportive person for your daughter to come out to!
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I came out as bi in my second year of university, but by my mid-20s, I'd changed my label again and started calling myself "queer". This wasn't a change in who I was attracted to, just how I described myself—I'm not going to go into all the details, but there's a lot of not-always-friendly debate within the LGBT+ community about whether "bisexual" or "pansexual" is the better word for describing attraction-to-more-than-one-gender, and picking "queer" was partly a way of opting out of that debate.
At 28, I met the woman I want to spend the rest of my life with. We've lived together for a number of years, were planning our wedding before the whole COVID thing ruined large gatherings, want to have kids together, and so on & so forth. I often casually refer to myself as "gay" these days, because it's a useful shorthand for "the only person I'm interested in romantically is another woman"... but I still appreciate the eye-candy factor of a good-looking guy in a well-fitted suit! And if I ever did find myself back on the market for some reason, I'd consider dating men, & would probably go back to calling myself "queer" or "bi" 100% of the time.
So... lots of changes of label, but far fewer changes of who I actually am or who I fancy: mostly just changes in how I describe those things to the wider world. Like me, your DD might take a while to figure out how she wants to describe herself to others; I think the best thing you can do is be patient with her while she does that figuring-out.
Oh, and @Whiskyinajar, I love the response you gave your son! "'I've simply said his feelings are normal for him and to talk to me if he wants to discuss it any further" = perfect