If shes working on a fwd walkover, get her to do loads of backbend into bridges, and then stand straight back up again, it uses the same stomach muscles needed to stand up out of a walkover, and although in a real walkover she will actually be doing it on one leg, it still helps to get the feel, and increases core strength.
If its bk walkovers shes struggling with, but she already has a bhs, then make sure she doesnt "jump" into the walkover. You have to get the timing just right, and your hands need to touch the floor before you push off the floor with your leg. This is the opposite of a bhs where you have to jump then hands touch, so it could be confusing your CP.
Apart from that, just make sure she has enough shoulder and back flexibility! Good Luck and I hope this helps! :)