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It is difficult to directly compare her benchmark score with the ITBS, as the benchmark is likely a criterion-referenced measure specific to your district and it's implementation of the curriculum, while the ITBS is a norm-referenced instrument. A norm-referenced measure doesn't technically tell you the grade-level performance of a student. Rather, it indicates that this student received a score at or above that obtained by this percent of the standardization sample on the same item set--which likely is not fully representative of the curriculum standards. It's a sampling for determining ordinal placement (rank order in a population), not for determining actual performance in a curriculum of a certain grade level. Though we don't know for certain, it seems more likely that the report card score is aligned with mastery of the curriculum standards for a particular grade level (at least, hypothetically), since it's based on performance in response to instruction in the whole grade-level curriculum.
Do you have information on the appeal process in your district? That would be the place to start. Almost every system is required to have a written appeals process, even if they don't publicize it.
