Advice for mum of 16 year old girl on cusp of diagnosis

Where to start! Really just wanting to hear ANY advice as we have been fumbling around in the dark from one diagnosis to the next for the past 3 years. 
We are half way through a private assessment but they have indicated an autism diagnosis will be given next week. My daughter is 16 1/2 and just about to do her GCSEs.

She has not been in school for much of year 11. Mostly a reduced timetable but in the end hasn’t be able to cope for even an hour. We will keep her at home now and she’ll will just go in for exams. School have said she can be in a small group of 6 and will have up to 30 mins break time. Which is good, although we would prefer a room on her own with her own invigilator. Has anyone achieved this?

We first noticed a change approx 3 years ago, year 8 of secondary school. Around the same time she lost both grandfathers, had a friendship falling out, and had a friend who was self harming, she was then self harming herself. Once we had been made aware of the self harming, she began weekly counselling and also had 6 sessions of CBT online via camhs. The situation continued to deteriorate, we changed therapists as she had become too attached to the original lady and wouldn’t talk to her and also paid for a private psychiatric assessment. She was diagnosed with generalised anxiety disorder and depression and put on anti depressants. A couple of months ago she took an overdose. By chance a specialist we were seeing for her persistent knee pain mentioned autism to us and we arranged an assessment. Hopefully this diagnosis will help our daughter understand why she feels how she does. She is also starting individual and group DBT sessions.

Are there any communities online or in Oxfordshire/Bucks area for 16 year olds?

How do you speak about the diagnosis after it has been given?

Any tips for managing the transition to sixth form/college and getting through the exams?

Any advice gratefully received!