Third spaces are the compromise solution.
I can’t really see any other approaches that keep all pupils (girls, boys, pupils of either sex who identify as the opposite or as non binary) physically safe, respect the accepted standards of same-sex privacy & dignity while undressing, and minimise both the opportunities for social misunderstanding and opportunities for bullying a trans student.
Not that I believe these girls WERE bullying the trans student, but I bet 10 plus teenage girls all loudly telling you to go away in unison FEELS like bullying, especially if you’ve been told by your parents, your head teacher and the T lobby that the girls have no right to object to your presence.
Adult activist demands for ‘acceptance without exception’ are causing the situations that harm the very children they claim to be protecting.