The article is clear that this is a boy who has been "socially-transitioned" at school as a girl since age 10-11.
I imagine this is happening all over the UK, not just boys being admitted to "all-girls schools" but sex-falsification both ways in mixed-sex schools.
The closing paragraphs are quite chilling,
"My daughter, unsurprisingly, is now completely indoctrinated into this ideology – she believes a man can be a woman simply by announcing he is, growing his hair, wearing make-up and acting in a vaguely “feminine” way.
The school has taught her to accept a boy into her single-sex spaces who says he is a girl, or a man who says he is a woman – no questions asked. Her boundaries about what is acceptable and what she is entitled to in terms of her privacy and dignity are completely skewed."