I obviously am not familiar with your state testing so feel free to disregard my post. However, I would first check to make sure that it is actually an issue of your DD forgeting all the fraction concepts from last school year. Sometimes these tests can be a bit strange and other times it may be an issue of failing to provide adequate explanation/procedures in support of the answer.
It is possible that there is a big change from the 3rd grade test to the 4th grade test. However, given the endless spiraling in most elementary curriculum, it seems odd for a gifted student to go from a high score in 3rd grade to a low score in 4th grade. My point is to make sure that it wasn't just an issue of a bad test day for your DD or some other idiosyncrasy with the test first.
If your DD did in fact forget all the fraction concepts, it should not take very long to give her a quick refresher so that she will score highly. It would create unncessary stress for her as well as damage her self-confidence if she scores poorly and the school challenges her placement and it turns out that the other GT students score highly on the test.
