It’s a really tough transition op, and it can take a couple of weeks to settle down, and realistically I wouldn’t be panicking too much until Christmas because it just takes time.
I found both of our schools were very helpful, and were quite well prepared for transition problems, and had strategies ready to go. It wasn’t enough at times, but the goodwill surprised me compared to my own school days.
I coached dd in being friendly, but not expecting everyone to be friends, which helped her get a handle on things. I’ve also coached her a bit on how girls socialise and interpret cues, ie the importance of a friendly hello every day because if you walk past someone, ignoring them, they may conclude you’re no longer friends. Boys, by and large, don’t require proof of friendship, but girls do, and just having the rules of the game spelled out can make a huge difference
There are some good resources for autistic teens but just have a flick through yourself first because some encourage masking to fit in which isn’t ideal.
I’ve been firm that no major decisions can be taken in the first two weeks, because every start back is a nightmare. My ds responds well to a rule like that. But it also helps me keep my anxiety in check because it’s a tough thing to navigate as a parent too.
Also, I let them know they can go in late, and home early but days off need to be pre planned. There’s enough scope in that to take the pressure off, and stop the school refusal being a power struggle between me and them. (But I’m not in the UK and the school have some flexibility to work with me on attendance so that might not be an option). Mine would often prefer to go in on time, than stand out by being late.
I’ve found that I need to strike a balance between sympathising and encouraging. I let them know it’s hard, but I that believe in them, that they can do it, and that figuring out what is needed is a three way collaboration between them, the school and myself.