I'm guessing she's on tranexamic acid? Does she feel better now or does she still have problems.
Hopefully CAHMS can be quickish and she can get some good counselling, maybe try and push for something like DBT over cbt. When is the meeting with HOY? I'd write a list of all the issues she's having in some detail and also what you think could help in school and the accommodations you want. Then you can discuss some of the accommodations and their ideas as well.
@Talkingfrog I actually a few weeks ago, saw some new research and essentially found that girls are excited for secondary unlike boys. But they have a massive dive in wellbeing from mid-laye Y7 and in KS3. It's partly because as some posters mentioned undiagnosed SEN, especially for BAME girls, they're less spotted as well as struggling.
Then they also start saying the misogyny from boys really skyrockets, and the feel shame, embarrassment, less smart and stupid, start saying that maths, science aren't girl subjects and the same for P.E. This behaviour happens during lessons and online and also more interrupting girls and talking more in lessons by filling up the space. It impacts their confidence and self-esteem and continues to reduce.
Then it's also periods and lack of education and openness on periods and menstrual health, they're told they are being over dramatic if they struggle with it during school. When we know periods bring headaches, diarrhoea or bowel issues, pain and cramps, tiredness and mood swings etc. They aren't supported through this and schools and teachers aren't empathetic about it and don't provide support. Those are the main issues specific to girls. The other things poverty, resource access, curriculum also has an impact but obviously not girl specific.