I'm not sure exactly what you are describing. Is she landing with the toes of both feet pointed in the same direction, and her belly facing the side instead of back toward the end of the beam she came from?
A lot of my girls have told me they pick a plank of flooring on their wood floors at home to use as a practice beam for cartwheels.
I recommend you find something for her to use as a line at home, duck tape on the carpet, whatever you can find and that she practice literally hundreds on the line at home. It will help if she can create the muscle memory of kicking the cartwheel the same every time and landing the same every time, shoulders and hips square, belly button toward the end of the beam, arms high and tight to the ears, eyes on the end of the beam. If she practices this with a lot of discipline, very tight body, holding the end position in a tight squeeze for 3 sec. each time it should help.