The school's explanation is actually not totally bogus. In fact, if you take the MAP repeatedly, you do run out of higher-level items eventually, which can artificially flatten or lower your score. There is a fairly deep pool of items for middle percentile students, but not that many extremely advanced items. Once you've used them, they're out of your rotation for future administrations for several rounds. (I can't remember the exact lock-out period, sorry.) Re-setting her MAP history will take care of that problem, but will also result in re-setting her start point to one grade level below her nominal placement, which can also depress her apparent performance level, as she might not have enough items administered, to make it to her true level, if it's very far above grade placement.
Have you tried out-of-level testing on something other than the MAP? E.g., the ACTs.
