As is often the case in response to posts like this, I have opinions, but nothing useful or practical to add!
I find myself focusing on the fact that it is a girls' school. I attended an all-girl's school and I think it was very beneficial in lots of ways, even though I stuck out like a sore thumb because I was very gender-non-conforming, perhaps to the point of gender dysphoria, if there is such a thing.
I had a range of role models of strong women (all the teachers were women, a mixture of nuns and 'civilians'). The person who taught civics was a woman. The person who taught us about our Gaelic culture was a woman. The person who taught science was a woman. The person who taught maths was a woman. The person who introduced us to our first foreign language was a woman. And so on.
So even though I didn't like being a girl, and dreaded growing up to be a woman, I could see that 'being a woman' could mean being knowledgeable in a whole range of subjects, from physics to 'Apologetics' [as RE was strangely called.]
In other words, being in an all-female environment, while difficult for me, at least showed me that there were different ways of being a girl, and I didn't have to be a boy to be scholarly, even in STEM subjects.
So the idea of girls in a girls' school opting out of being a girl is problematic for me, and for the school to encourage it implies that they are sanctioning a stereotyped definition of what a girl is.
Not very practical or useful, sorry Aethelthryth! but there's a voice in my head saying 'it's a girls' school, for fexsake, that has to have a meaning, an ontology, a teleology, or something ending in -ology!' 