I can tell you what it means to our school. DD is in 4th and will take it next week as a further step to being admitted to the GATE program. She scored very high on the MAPs so this is the next step.
CoGat stands for Cognative Ability Test and is supposed to measure non-academic based intelligence, as opposed to the MAPs or ISATs or other state tests that measure achievement.
Has your DD had any contact with your GATE teachers? Maybe they are considering her for admission. Regardless, I would email the principal and ask why she took the test. In my experience, because it is not academically based, it is not used as a benchmark for the school.