I’m really sorry she’s going through this.
I do have experience as my daughter has gone through something similar, albeit it started when she was younger.
To be honest there weren’t and aren’t any quick fixes.
Start the ball rolling now on all the things that will take a while to put into place. Access CAMHs via the GP AND school. Get any school counselling or school nurse help you can.
At the same time look into mindfulness and breathing. Sounds woo but it’s helped my dd.
Talk to your dd and explain that the physical symptoms are very real but caused my her emotions, it’s fight or flight.
With my DD it helped to get her into school a bit later than everyone else but collect her after hdd as LG an hour. This increased every day.
I’d like DD to have a lesson leaving pass and a break out room to go to but that’s not available at the moment. It’s worth asking the school though.
Rescue Remedy and sucking ginger tablets or drinking ginger tea.
A good mind trick is to do the 5,4,3,2,1 Senses game. Name 5 thinks you can smell right now, 4 things you can feel, 3 things you can see, 2 things you can hear and 1thing you can taste.
Don’t worry about breakfast but provide cereal bars, croissants and juice for break time.
I’m sorry you’re DD is going through this. Hopefully this will bump you’re thread and you’ll get some better answers.