Also important to note: what when it's not a child who has been a part of the group from an early age, but is a child that reached their teens before socially transitioning and the girls in the group are expected to change with a teenager who they have always known as male?
This is the same argument often used for single sex spaces with pictures of very feminine, young and vulnerable TW meant to attract the sympathy and understanding of 'how could you be so unkind as to not want to look after that feminine person', where if the photograph or video showed an older, adult transitioned TW such as Danielle Muscato complete with beard and the 'suck my lady dick' tweets, women's varied responses would be immediately comprehensible.
Solutions are needed that work for everyone. And that means additional spaces for those who would prefer not to use sex based spaces, and also that some women and girls need single sex spaces.