Ughhh...never mind. I don't know what I was thinking - I'm a 21.5 Mondo, which translates to a size 3.5-4. My apologies.
Regardless, if there is a significant amount of space between your bare foot and the edge of the board, turning ability would be sacrificed. If she is having a hard time on a Ride Compact, which is not a stiff board, she will need to experiment a bit.