I know a trans person who voted Trump in 2016 because she hates Hillary Clinton with a passion that outshines even this whole site. People have their reasons.

More importantly: would it really have been better if she told you she votes dem? Both parties suck equally. Unless she specifically votes against one of the rare good candidates, there is so little difference that you shouldn't care. I'd use it as a jump-off point to discuss politics and maybe give her some actually good views. Not in a heavy handed way of course, you gotta go slow there, or you might come off as a crazy person to her.