OP, if you’ve got time you might also want to look at the Transgender Trend website:
www.transgendertrend.com/
And there’s also the Safe Schools Alliance, which might be a help if you feel there is anything you want to tackle with the school:
safeschoolsallianceuk.net/
Do you know if the school staff are “affirming” them, ie changing names on the register, using male pronouns in class, or is it just their friends they are expecting this of?
In an ideal world, you would be able to speak to the school and they would recognise this as a form of social contagion, and perhaps have an assembly on the dangers of peer pressure and spending too much time online obsessing about your “gender identity”.
But sadly these days schools are more likely to be the ones promoting the concept of “gender identity”, and even if they’re not doing that, they probably won’t want to say or do anything that could possibly be seen as “transphobic”. And the current definition of “transphobia” is pretty much anything that isn’t full endorsement of transgenderist ideology around gender identity etc. So you may not find them very receptive if you do approach them. But it’s worth thinking about.
It really must be so confusing for your DD, feeling like the girls she thought she knew are all morphing into strangers, and also feeling excluded given that they’re all talking about this all the time. No wonder she’s upset.
On the bright side, Y7 is a time when most children start branching out and making new friends, and there will be lots of social flux going on in her year group now in general, so maybe you could encourage her to focus a bit less on this group of friends and be open to forming some new friendships.
Also let her know she doesn’t have to go along with this - there are an awful lot of people questioning this whole phenomenon and it’s not the simple case that “respect my pronouns = good, forget my pronouns = bad”. Encourage her to think critically about this, with you at least.
Good luck to you and her.