She struggles with social situations, crowds and new experiences. She needs to be told step by step instructions for anything she’s not done before and isn’t great with taking the initiative
Generalising here, this is where a LOT of FE falls down for autistic kids, they are expected to go to their support and tell them what's causing them difficulties and ask how to get around that, which no doubt an NT kid of that age could do, but for my autistic dd at that age, it was a step too far. She couldn't identify what she needed help with, so that didn't work for her.
I'm so sorry you've been told she has 'mild' autism. as you can see when she is faced with dealing with a change, her autism is far from 'mild' To obtain an autism diagnosis, she needs to have " “persistent difficulties with social communication and social interaction” and “restricted and repetitive patterns of behaviours, activities or interests” (this includes sensory behaviour), present since early childhood, to the extent that these “limit and impair everyday functioning”. Source www.autism.org.uk/about/diagnosis/criteria-changes.aspx
There's also a good explanation of 'mild autism' here theaspergian.com/2019/05/04/its-a-spectrum-doesnt-mean-what-you-think/
"My doctor recently referred to my autism is “mild.” I gently pointed to my psychologist’s report which stated that my executive dysfunction as being greater than 99th percentile.
“That means I am less functional than 99% of people. Does that seem mild to you?” I asked her. But, you see, I can speak, and I can look people in the eyes, so they see my autism as “mild.” My autism affects those around me mildly but my autism does affect me severely."
Right now, I'd let her proces her experience until she feels able to try doing something different. Do remember that emotionally she's likely to be only two thirds of her chronological age, so do alter your expectations about what she should and shouldn't be able to cope with 'at her age'
Have you applied for PIP for her? If she's getting DLA, then the transfer will be activated when she's on their list, no need to apply now to change.
Is there a Carer's group in your area? Your local Council should have details, contact them and ask if they have any advice, they may well be able to give you contact details of an Autism support organisation near you, ask if there's anything for teens.
Are you on facebook? I'm not but have heard posters here say there are a lot of support groups on there, so you could look for any in your local area.
When she's fully got over that experience which could likely be months not weeks, could she study using Interhigh if she finds anything of theirs interesting? Lots of parents whose kids can't survive in mainstream have posted on here about it, so it's worth bearing in mind for the future. interhigh.co.uk/