I have one piece to add to this. An evaluator will not raise a red flag as long as both of your child's scores on the WISC are normal or above. A trained neuropsych evaluator probably would, but the school evaluators are only concerned with whether the child can function in a normal classroom and whether they meet the criteria for Gifted.
That said, you should be concerned if the difference between the two scores is a standard deviation or more. That is a sign that your child might need to be looked at more closely. ADD might be one answer, since they need IQ tests broken up into smaller chunks. Another answer could be seeing a developmental optometrist and making sure that she focuses well and that she has good binocular vision.
My DS6 had similar issues on the IQ test. After some vision therapy and having the IQ test broken up, his scores are more even and very much reflect his capabilities.
