Was she taught to "start them hands", or "knob to the ball"......? Or maybe she doesn't get her hips turning ahead of her torso..?
If so, she's likely swinging on a downward path with a cast... just a guess without a video
Without seeing, a good way to stop lunging is to tell them to get into their front heel. You can only lunge if your weight is in your front toes. Tell her when she swings she should feel her weight in her front heel and try to get her to lift her front toes off the ground.