I have a 7 year old DD going through the very slow diagnosis process. I also have an Autistic DS (full EHCP in special autism provision) and an NT DS. With DS1 school supported the whole diagnosis process. With DD she's not disruptive enough - but I'm working with school to keep a decent paper trail should we need to go EHCP route. She wouldn't meet thresholds at present.
I'm just wondering if you've managed to engage with the headmistress over this is there are other ways/ ways in parallel moving forwards to help your DD so I'll list so e of the things that have helped us.
I'm keeping my own folder paper trail to show the extra support DD is having. Every school meeting, whether it's a discussion at the door or sitting at the desk, I email a thank you for meeting and sumarise my understanding of any actions from the meeting.
I have chatted with the SENCO about padding out DD's SEN file and she's been great at adding extra notes.
Have you had any support from speech and language? They've been great with DD and I have been in and done talk about training so have several of DD's whole classTA's. They do regular small group work with DD on social communication. They storyboard events with her to help her look at things that have happened and look at how they could be approached another time. They have also produced assessment reports. My favourite little quip was DD was shown classic happy face and sad face emoji type images on A4 sheets. She was asked about how they feel. After much deep consideration and with a furrowed brow she responded 'like paper'.
In class, DD has her own quiet desk (since yr 1) that she can go to to do her work if feeling overstimulated, she has tried ear defenders but doesn't like them, she can go to the book corner or library if she needs quiet time at break, sometimes she eats her sandwich in class with the TA/ teacher rather than the dining hall. Her teacher writes the days activity list on the board. In year R we used words and pictures to create a week timetable. I'd run through it each day with DD before school and she had a copy in her book bag.
Other early school life little adjustments that made life more comfortable were having her peg at the end of the coats so she didn't get into a scrum with other children, same with her tray, being encouraged to go to the toilet/ go get her water bottle/ get her coat 2 minutes before the rest if the class were sent - again to avoid the rush.
Budgets have been so significantly cut in the last few years that support available for our elder children isn't their for those entering the system now. It's a whole new game to play. Gool luck.