The drive is good but it's held back by the back heel anchor she is dragging along. Without the heel off the ground and turned she can't properly release her hip at release.
Try not to take the upper body back so far during the first step. Establish forward lean early. I like to preset the forward lean with our butt out and forward lean already established
To elaborate a little further as I didn't have much time this morning....
The purpose of the two step drill is to teach the pitcher how to establish a sprinter's posture, or the first "h" of the double "h" concept.
Notice your DD here:
All she has essentially done is step back and pull her entire body back to the back foot. She is almost stacked over the back foot as if she had never stepped back. The purpose of stepping back is to train a sprinter's posture.
Like this:
Work on her getting into this more explosive posture here. In other words, as she steps back and as soon as her toes hit the ground, she should start her entire body forward in an aggressive manner.