Would anything in this article help make a case?
https://www.nagc.org/sites/default/...s%20Receive%20Appropriate%20Services.pdf
Does the PsyD have 2E expertise?

It's difficult enough trying to advocate in an educational setting. I don't envy your situation. If the other parent is open (:/), sometimes relying on someone with expertise to do the explaining can help mitigate ego fallout.