The reason her drop isn't getting the big movement is because she is letting her right hand come up. The hand needs to be pointed to the ground as much as possible during the release.
It might help to have her to think about "screwing the ball into the ground" at release.
This is the drill my DD did to perfect the drop release. When she wasn't getting enough "bite" on the drop, she would do this drill.
<iframe width="560" height="315" src="https://www.youtube.com/embed/LDU6KNYVgEE" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>
The 1st, 4th and the others are when she did the drill correctly. Note that the ball bounces almost up with top spin. The last two times she did the drill are perfect.
The 2nd and 3rd throws are *WRONG*. The ball goes forward with top spin, not up.
Note that her arm starts at 7 or 7:30 to do the drill.
You do not roll the ball over the hand like this. Get a good camera and learn the truth