Explaining the ASD assessment to a 9 year old

Hi, my 9 year old daughter has suspected high functioning autism and SPD, we have her assessment coming up and could do with some advice on how to broach the subject and explain it to her. She's not aware yet these assessments are happening and I'm aware they will mention autism, so will need to explain that to her too. She's likely to get very upset and angry, so I was thinking of addressing it more from the angle of 'Mummy and Daddy want to be able better understand how you might feel sometimes and what we can do to help... '

We've also been offered ELSA sessions at school, but she masks at school, apart from 'OCD/routine' type habits the teacher has picked up on so it's not necessarily an issue within school . She mentioned a friend who was called out of class every week to go and speak to a lady, she said she thought it was because this girl is shy and doesn't like to talk to people. I then used this lead to ask her if she ever thought talking to someone else sometimes might help her, and she got very angry, shouting how she is happy at school, why would she want to do that.

Does anyone have any help or advice on either aspect and maybe share their experience?

Thanks in advance :)