It does sound as if she may be in burnout due to the prolonged pressures of attending school and not having her needs supported.
professionals as saying she needs to attend school and see professionals involved
It's likely they don't fully understand how overwhelming this would be for her in her current state. It is attending school that has caused the problems in the first place and going back without adequate support in place is not going to work.
Any meeting with professionals should happen in an environment in which your daughter can feel safe. Would she possibly be open to appointments by video call? That can be a lot less overwhelming than an in person interaction.
we gently told her the lady was here to help. As soon as the lady spoke to her she seemed to mentally freeze, ran into the dinning room and I found her on the floor in the corner facing the wall unable to move or speak.
That's sounds like an autistic shutdown, a response to being severely overwhelmed.
The situation is not easy by any means and results from the build up of years of lack of support and resultant stress on your daughter. It is so important that your daughter is allowed to progress at a rate that is comfortable for her. Attempts to push her too much while she is in burnout will have the kind of negative results you have already encountered.
Don't be afraid to trust your instincts. You know your daughter better than the professionals do and they do not always have appropriate understanding of autism. CAMHS sadly have somewhat of a reputation for making the mental health of autistic children worse rather than better.
https://emergentdivergence.com/2023/11/14/camhs-crisis-an-autistic-parent-speaks-out/
These websites may be of help if it is autistic burnout:
https://autismunderstood.co.uk/struggling-as-an-autistic-person/autistic-burnout-what-helps/
https://neurodivergentinsights.com/blog/autistic-burnout-recovery