Huh, I missed that. I thought it was EY's way of dropping in a cultural tidbit about the wizarding world, where a transsexual girl is naturally thought of by everyone as a girl, though they all know that she makes her body the way it is by being a metamorphmagus, and she reverts to her non-metamorphed form when she's startled. Then I started wondering what non-metamorphmagus trans people would do. Maybe there are permanent sex-change potions. Or perhaps temporary ones that you have to keep taking, like polyjuice but without copying anyone. Or maybe all trans wizards are metamorphmagi, but I doubt it.