Litter box issue #1: Medical problems.
Cats with medical problems commonly begin eliminating outside of their litter box because they begin to associate the litter box with a painful symptom caused by the illness. So the first step is always a trip to the veterinarian to rule out any medical issues.
Litter box issue #2: She just doesn’t like it anymore.
For whatever reason, your cat may have decided her litter box is an unpleasant place to eliminate. Here’s what to do:
1.Keep the litter box extremely clean.
2.Scoop it at least once a day and change the litter completely every four to five days.
3.Add a new box in a different location, and use a different type of litter in the new box.
4.Make sure that the litter box isn't near a noisy appliance, or in an area of the home that your cat doesn't frequent.
5.If you have multiple cats, provide one litter box for each cat, plus one extra box in a different location.
The aggressive cat.
Whether it’s to tell you to stop petting, start playing or just that they’re afraid, some cats use their teeth to do the talking. Feline aggression should be taken very seriously and, therefore, requires professional help – either through your veterinarian or a behaviorist. It’s important not to punish the aggressive cat because punishment can make the problem worse, especially if the aggression is caused by fear.
