Never had a GF who had braces – not that I’ve had that many GF’s! (And the current one is probably going to stop being my GF soon and become my wife...)
The opposite was true however, I’ve had three GF’s as an adult while I wore braces. One did not care one way or the other, the other two quite enjoyed them. One of which loved my braces, said they reminded her of some steam-punk sci-fi device, and she said it made kissing that much more interesting, and the other would sometimes use my braces as a “bondage” device when things got interesting. Lost a game of chess against her, my forfeit was to wear my elastics doubled-up for the rest of the weekend. Ouch. (but fun!)
I did also have a “kink play partner” a few years ago that wore braces. Was great fun tying her jaws together using dental floss and then going out for a meal. Yeah, that’s evil – but she loved it.