Yes my dc had Wednesday afternoons off study to do sport and extra curricular activities in EU. It was great to decompress!
And there were approximately a third of the add-on activities involving costumes and trips out and fund raising that take place in a UK primary. A very packed and busy schedule doesn’t suit every child.
Also the walls and noticeboards etc were a lot quieter, or more boring depending on how you look at it, as compared with a UK classroom and there wasn’t as much group work. All of those things contribute to the busyness and overwhelm for a very young child especially if they have ND traits.
Having said that, your attitude will also influence how your dd perceives school op. I only say that because your dd asking for one day off in the middle of the week to rest sounds like a concept she has heard about from an adult but I am prepared to be corrected on that!
Also, different families can have very different energy levels and different tolerances of noise and chaos within the home. A child who is used to a very structured quiet environment with lots of time on their own might struggle more in a very loud, busy classroom.
One last thought; are you sure she isn’t being bullied or harassed by another child either in her class or by an older child in the playground?
I hope you find a solution that works for your dd op; she sounds miserable poor thing. Once you have done the medical checks, I would go to the head teacher if you are not getting anywhere with her class teacher.