Hi Boldly,
Is there a children's hospital anywhere near you? That's the route that gave us the best luck with diagnostic testing.
I think you're very right to pursue it-- a lot of the frustrating behaviors you describe would be consistent with autism spectrum disorders or ADHD, and you would need a very good professional to sort this out.
Because she's a girl, and that bright, if she has autism it's likely to be missed by a tester who hasn't seen lots and lots of girls on the spectrum. Girls present in subtle but important ways; schools often think they're well behaved and just a little disorganized even if much more is going on under the surface.
Because of that, were I in your shoes I'd probably seek a diagnostic center that specializes in autism spectrum disorders to rule that in or out; such a center is likely to also have lots of experience in teasing out attention issues from spectrum issues, because they deal with the borderlines between those diagnoses all the time. They would undoubtedly include IQ and achievement testing as part of the battery of diagnostic tests, so you'd get a pretty comprehensive picture.
Best,
DeeDee
