Not knowing what your specific quibble is, I'll describe both what you might expect from standard uses of the IAS, and some possible irregularities.
Academic achievement testing typically is scored both using age norms (the actual age of the child) and grade norms (the grade of the receiving grade, or one or two grades up--in this case, using first grade norms), to see how they compare normatively both with their age peers (these are true norms) and with their prospective peers, since the objective is to place them into the upper end of the receiving grade, not the struggling end. Both results would be reported as standard scores or percentiles (or some other transformation of z scores). So there should be two places where the same WIAT-III results might be entered, but using different numbers.
Achievement: based on her current grade (or age, if she is typical age-for-grade right now). These would be expected to look much more like what you've experienced in the past. Typically schools are looking for results at 90+ %ile (or higher, depending on the local population; 95th %ile is also common).
Aptitude: based on the grade of the receiving cohort. These would be expected to be substantially lower than you've historically seen. Typically schools are looking for 50+ %ile (75th %ile is also fairly common, again depending on local population).
There are some who interpret performance at least two grade levels up as meaning grade equivalents from achievement testing two grades up. While this is not an unusual interpretation, it is, as you may be aware as a person with some statistical sophistication, not a psychometrically sound one. The problems with using grade equivalents with instruments like the WIAT-III have already been thoroughly discussed numerous times, including elsewhere on this forum.
It may be that your school system has instituted policies for acceleration that require personnel (i.e., the school psych) to work through the IAS criteria in a way that may not be psychometric best practice, which may or may not be something the psych agrees with, but certainly isn't something they could comfortably disagree with publicly, let alone to the parent of a student in the decision-making process.
Whatever the nature of your doubts about application of test data, until you know where the decision to apply them that way originated, it will be unclear whether, how, or with whom, to address them.
