I, too, have a girl with inattentive type ADD who I was told by many could not have ADD. She, too, performs well above average in school and has some areas even on group tests where her performance is outstanding (got 800s -- as high as the test goes -- on a few parts of the CSAPs [Colorado NCLB test] such as vocab, algebra, etc.). We even had one of the psychs who saw her say that it wasn't ADD and she was someone w/ experience in LDs. The one who recognized it was a psych with experience in giftedness and higher levels of giftedness.
I have two thoughts based on what you've posted thus far. Was comprehension a low outlier on the Verbal index of the WISC? It definitely was for my dd. I've been told that a low comprehension score is more common in ADD as well as ASD. My dd is very, very socially aware -- to the point that she trims herself to fit in so well that almost no one knows the true kiddo -- and I am pretty confident that she is not on the autism spectrum. However, your last post in which you mention that your dd's behavior appeared young and that she does things that scare off other kids had me wondering if you'd considered aspergers.
I found Dr. Webb's book, Misdiagnosis & Dual diagnoses of gifted children & adults, to be really helpful in seeing whether my dd was 2e or just underperforming due to poor fit. She was the opposite of every single thing he listed for a gifted child who didn't have ADD. I believe that book also has a chapter on ASD if that is something to rule out as well.
