We have two cats, both females. One's getting up there in age and the other is about two years old. The younger cat enjoys attacking the older cat, climbing on top of her and biting her in the ear, chasing her around the house, butting in front of her at the water dish or food, etc. The older cat just puts up with it, doesn't put up much of a fight. Lately however, she hasn't been using the litter box properly. I read on another site where it said, "If you have more than one cat, is the cat in question intimidated or chased by one of your other cats? If so, the scared cat might feel too vulnerable to use the litter boxes in the present location." This is very much the case. What can be done to get her to use the litter box again?