I wouldn't say that her PSI is actually bringing everything else up, but it may be confounding assessment of her actual rate of learning with the pace of work completion.
I do want to note that, even if her "actual" rate of learning is not technically GT, she is still clearly a bright little person, capable of functioning beyond her nominal grade level. If you consider how a typical classroom is designed, the expectation is that students will largely fall within one standard deviation of the mean, ranging from the low end of average (about the 16th %ile) to the high end of average (about the 84th %ile). Functionally, this encompasses about a half grade level below nominal grade level, up to about a half grade above. A child above the 90th %ile (who is often probably a grade level above) thus falls outside of the differentiated instruction range for which standard textbooks plan, and will need more than the teacher normally provides--even though 98th %ile is where the GT classification formally kicks in in most places. So a nominally non-GT child may very well need GT-type planning.
All this to say, the specific numbers are not as important as whether your child is happy, engaged, and optimally challenged. If she needs more academically to reach that point, which side of the cutoff she falls on is not the critical question.
