In my (limited) experience: the neuropsych is mainly for testing. They know all the tests available, decide what to deploy, and are expert in reading the results and diagnostic work. They should be able to sit with you for some hours after the testing, tell you exactly what they found and what it means. They should generate a nice written report that helps you get services if you need them.
We use a dev ped for ongoing skilled care for DS9 with AS. She is in charge of meds, and she is in contact with his case supervisor/therapist to talk about what we are seeing and what needs to be addressed; they work together. She knows things a pediatrician would not dream of, she's seen and treated zillions of kids with DS's type of issues-- she is the ongoing expertise that helps us steer treatment.
In your shoes, for the eval, I'd look for a neuropsych who's seen tons of girls with AS, preferably also gifted and ADHD, so they're used to differentiating. Based on what I've seen in your posts, I'd want someone with lots of AS kids in their experience, as that's the hardest differential diagnosis to make in a gifted girl. (i.e., they get missed/underdiagnosed most). That way, if they rule it out, you're sure.
HTH,
DeeDee
