Ability and achievement tests really aren't testing the same thing. Deborah Ruf, who is an expert in testing of gifted children summed it up well in an article that is being discussed in a recent thread here, "The WPPSI-IV Technical Manual points out what many of us know, too, that achievement scores often have more to do with exposure and opportunity and don’t necessarily identify intellectually gifted children."
That said, I really hate the CogAT and wish that people, including the aforementioned Dr. Ruf, wouldn't refer to tests like the CogAT and OLSAT as "group IQ tests" b/c the test publishers have stated pretty clearly that their tests are not intelligence or IQ tests and are not meant to be used as such despite the frequency with which they are.
Would the district consider outside testing? Can you afford to have your dd take an individual IQ test like the WISC or SB-V?
I think that you've got two possibilities here:
1) your dd is a high achiever but not gifted and, yes, I have seen kids score in the 99th percentile on achievement tests and have dead average IQ scores
2) your dd is gifted and the group test is a poor fit for her. I've also seen this particularly with divergent thinking gifted kids and highly gifted kids who may come up with answers that are more complex than the test designer had in mind with their multiple choice test.
