You could also add in some basic groundwork exercises.
Get her backing up in hand, make sure she has her head down and her butt under, then she will be using her back, a few slow correctly carried out steps is far better than a 100 with her hear in the air and hollow through the back.
Also get her turning on the forehand, in hand, keeping her front feet in place, get her to move her butt over, you are looking for the foot that is moving to step in front of the static one, if she is doing it correctly you should see her back muscles working. One or two steps in each direction to start with, again quality is better than quantity.
Once she has the technique and form correct you can ask for more and more repetitions.