Do you have to be a feminist to care if little girls feel comfortable?
Yes. If you care about little girls feeling comfortable, and follow that line of thought, you will inevitably end up becoming a feminist.
FGM, sexual violence, beauty ideals that require girls to completely alter their natural bodies ... it is all very uncomfortable, isn't it? I mean, most of it is worse than uncomfortable, but it is also uncomfortable.
To all those who say "You knew the rules!", you know damn well that to ordinary people, there's no unlimited choice between schools to send their daughters to. So, would you prefer if a) British women aborted female fetuses to prevent their daughters from being forced to wear skirts b) just didn't have any children anymore c) just shrug and not send their daughters to any school whatsoever, resulting in having the child taken away and placed in foster care and THEN being forced to wear a skirt for school?, or d) do you want all girls who don't want to wear skirts given testosterone, having their breasts chopped off and forced to use the boy's changing room, boy's showers and boy's toilets?
Those are the options you get.
Which of them do you prefer?
Or does it, now that you think about it, appear like a better idea to just sue the school for being sexist?