Make sure her stride is not too exaggerated, or long.
My DD has a tendency, when she strides too long, to hit under the ball about an inch below where intended. Causing a lot of fly balls.
We suspected it was the dip in her hips which she did not account for and her hand eye coordination to the ball.
We shortened her stride which kept her hips more level and brought her to the ball better.
Thanks for the information. Actually the stride is very small and subtle, but thank you