Not sure what you mean? Is she pushing during contact? Is she getting to the top of her toes? I'm sure someone will post a video of the back foot at contact, but if she's lifting her heel to get more "on toes" during contact than that's not causing the pop up. That's a normal part of making contact.
I'm sure one of the experts will provide more guidance.....
I will try to gt it on video. I do understand that the heel will be off of the ground at contact. This is more like she is pushing up instead of rotating around. She doesn't do it all of the time but when she does it does cause her to hit pop flies instead of line drives. It is not a huge issue I just can not figure out why she does it. If you tell her what she did she corrects it as well, which is cool in BP but not during a game.
My DD had this problem. We practiced a lot of front toss with the TCB hole balls. We practiced enough that she was able to recognize the feel of the correct movement vs the lung movement. If she would lung, we would stop and discuss. She seemed to lung when she was early on her swing and was already committed to swing (actually started her swing) and to make contact since she started so early she would lunge and hit the ball way out in front. She would also lung when she read a high pitch, this was a result of dropping her hands and trying to use her body to get back up to the ball.
Like Eric said, without video, we are taking blind shots at the root cause.
Guessing like the rest without video. Like knight posted your DD is possible dropping her hands. Then in order to get the hands and bat back on plain with the ball your DD may be raising up on her rear foot.
She would also lung when she read a high pitch, this was a result of dropping her hands and trying to use her body to get back up to the ball.
I will try to get a better video tomorrow. I went through my files and didnt have any of a recent swing other than this one. It may not be of any help. Thanks for the replies anyway. https://www.youtube.com/watch?v=-xRzWnO9tnM