You might try having her stand squarely on the pitching rubber facing the plate. Have her hold both arms down to her sides. Grab her shorts, shirt or something to keep them there. Without moving her arms have her drive off the rubber (keeping her trunk upright), flexing her right knee for additional drive. As she is driving off have her close her hips to the plate and drag her drive toe. She will find it very difficult to bring the drive toe off the ground without the arm momentum to aid in the lifting. This will give her a feel for the concept of dragging that toe throughout the motion. This will also give her the feel for maintaining her balance throughout.