Sorry for the delay, I had to collect her from a sleepover and she's been absolutely manic all morning and is now in a Minecraft trance.
I haven't read all the replies, still catching up and will read through them when I can.
Just to answer a few questions and clear some things up...
We are in Scotland. The process so far is that I called the school to arrange a meeting, the assistant head set up a meeting and asked me to write down everything I could think of about DDs behaviour, habits, likes, dislikes, meltdowns, anxieties, etc in order to pai t a picture of homeDD as opposed to schoolDD. I did so and went to the meeting and when finished she said she thought ASD and ADHD and she'd make the referral straight away. I then received a letter with a questionnaire which I completed and returned. However the questionnaire just wanted straight forward answers and DD is complex so it was difficult to answer, plus there was lots of questions about her behaviour at school, which of course I answered truthfully because she's not disruptive, she can sit still, she does engage, but it's all because she's masking! As soon as she is in the car on the way home from school, she starts spiralling.
As a result of those answers, the letter I received saying there is not enough evidence to go froward to the next stage of the process because she's fine at school.
Do it looks like we definitely have some options, thank you so much for all your helpful suggestions. And just your kind words and support.
To answer another couple of points, I don't want a lable for her, I want support in place before she goes to high school. She is a lot like me in that I was a perfect primary school pupil, I had a difficult home life, my parents were not particularly nice to me ans I always felt like I wasn't really liked and a difficult child, I guess I acted a lot like my DD at home. High school was too much, I was in all the top sets and loved learning, but struggled to study at home, struggled with focus and time keeping in my exams and didn't do as well as I hoped. I also developed and eating disorder, started self harming, and started doing some pretty dangerous things like jumping into a rover I knew to have bad currents, having unprotected sex, experimenting with drugs and alcohol, etc. I wasn't a bad child, but I hated myself, I was on antidepressants by 15, I completed school and applied and wa accepted to university, but I was crumbling and at 18, my parents kicked me out. Obviously I would never treat my DD the way I was treated and I will support her in a way I was never supported, but my biggest worry is that she slips through the cracks and there is no support for her other than her father and I.
Again, I am still reading through all the replies, but it looks like the next steps are to speak to the school about a referral to the Educational Psychologist, and also get a GP appointment for a Paediatrician referral. And above all, educate myself more. It's just a mine field but I will set some time aside to do all the research I need to do in order to help and support her as best I can.