Trans women are women, whether they hold themselves to your standard of transition or not. Please take care to create an accepting environment on your team for your new member if she decides to join.
Unfortunately lots of cis people are uncomfortable around trans people in private spaces. I’m picturing hotel rooms for travel events. How you deal with this will be touchy. I don’t have any concrete advice here except to discuss with your mentors, the student, as well as probably her parents and the school administration (if you have one), in order to find a solution that keeps everyone (including your trans student) comfortable.
If you have to make compromises, try to make sure your trans student is comfortable. You have an opportunity to create a safe and validating space here.