I don't think I would take any one test as definitive, especially if it conflicts with what you otherwise observe. It is just a single data point. Also, she is still very young - my DD did not take the CogAT until she was in 2nd grade!

Also, as deacongirl pointed out, some children who score very highly only other tests (including the WISC), do poorly on the CogAT. Your DD might do extremely well on other tests.