looking for advice on why my DD might be popping up.
... due to not firing the hips ahead of the torso. This will cause a dip in the shoulder and a dropping or flat barrel.
.... focus on the proper sequence of the hips leading the torso (aka "Elvis move" by Straightleg)
Pop ups typically occurs after a downward swing and the bat cuts under the ball.
SL, JBooth tried to explain to you that the reverse top hand drill that you were having your daughter perform was not resulting in her realize post impact extension towards the pitcher. If you slow the video down and look at it closely then you'll see that he is correct.