Are her comprehension tests the traditional AR tests that she takes on the computer? Or is the teacher asking her questions and waiting for verbal indication that she comprehends?

If it is the computerized AR test, then I would ask that she be tested orally and see if this changes the comprehension score. If it does then I would start to consider that either she is not a good tester or that she may have some trouble using the computer or might need an eye examination.

If you can't identify a problem with the comprehension testing, and you feel that her reading is not being challenged at school then I would probably chalk it up to an uncooperative teacher and do my best to work with DD at an appropriate reading range at home.