no reason why she would not be admitted other than a slight paucity of extracurriculars
On the other hand, in some schools/districts this would be a huge flashing light signaling a problem. If limited by finances or logistics such as severe illness of an immediate family member, there is a smaller but still meaningful number of extracurriculars in which a child might engage. Lacking that, there may be a presumption (right or wrong) that the child cannot handle extracurriculars while keeping up with her studies... which would be a huge problem if it is occurring in 4th grade.
... I can't imagine 4th grade scores will matter to anyone for high school
EXPLORE is an 8th/9th grade test, so in some schools/districts it may receive more than a passing glance for entrance to high school... even if retaken during the intervening years. As others have said, it is a great experience for a child to take an out-of-level test on which they are not expected to know all the answers. EXPLORE may be a more difficult test to "game" as you say, therefore some may see it as highly credible.
It's quite possible DD will not do all that well on the Explore
Sounds like performance anxiety of the parental kind. Meanwhile many gifted kids approach these tests with their intrinsic curiosity egging them on, like an itch that simply MUST be scratched: they want to learn what kids in the 8th/9th grade are asked about knowing!
