My DD is very nearly 7, and only diagnosed last week. Mainly because at school she appears to be the model pupil - takes instructions literally, follows all the rules, eats all her lunch, tidys away everything etc etc. however beneath the surface, and once the psychologist went in to observe her, and commented to teachers, TAs etc on things, they could finally see what I have said for the last 3 years to them, and for 5+ years to GP/HV/paediatrician!
We've had to battle hard to get her diagnosed, because girls can hide it very well, and especially in high functioning/mild cases, it's not always obvious until 10/11/12 years old.
We were fobbed off by a paed who saw her twice, for 10 minutes at a time. But I knew deep down something wasn't right, and pushed for more checks. Eventually I had to do a complaint, after being told I was just an over anxious mother!
This resulted in us being referred to the best Pyschologist in the county, and she has been amazing. She's been so thorough and after 6 months of meetings, assessments etc, we finally have the diagnosis - Asperger's.
Now we have this, we will be referred to a support team, who will write to school, explain it to them (part of it is they are just not trained to see things in the right way) and give them advice etc for dealing with more challenging years to come.
My advice would def be video as many different aspects as possible, record things, triggers, melt downs etc, but also fight for things. You know her best, so stand your ground and get her the assessment she, and you all, need.
I've now got the added complication of my husband just being diagnosed with Aspergers too! Good luck!