I'm 23 and not a learner anymore but even back when I was 17 and learning it wouldn't have bothered me. It's the kind of thing that I might be surprised to hear but then I would just get on with my lesson. I would never assume that because an instructor was transsexual that I wouldn't be able to talk to or feel comfortable around them. My impression of you, from what you've posted on here, is that you seem like a very competent and understanding instructor and that is what I would be looking for.
I agree with what others have suggested in terms of trying to encourage former pupils to give recommendations and trying to foster relations with LGBT societies which would surely create interest amongst members but perhaps also their wider circle of friends. I know it isn't easy but it would be such a shame for you to give up on something that you obviously enjoy and are good at. Hopefully the many positive responses on this thread have provided some reassurance. I respect you for raising this topic and genuinely wish you the best of luck.