Was she in second grade when she took the test at age 8? From kinder to second the test is read aloud to the kids and the format of the questions is different (more picture based). It is also untimed, and kids have to wait after each question for everyone to finish to move onto the next. From third grade on, it is timed and is more word and number based, except for the nonverbal section. Kids read the test themselves and move at their own pace until they finish or run out of time. The link below shows that types of questions that are asked at the different grade levels.
http://www.riversidepublishing.com/products/cogAT7/content.htmlMy kid took it in first, second and third grade and scores changed dramatically each time.
It could also be a difference in maturity/effort on the part of your child.
