Big litter box in dining room
(Alda, Nebraska USA)
My son's cat (female) is using the dining room carpet as a litter box.
I'm sorry to hear that your son's cat is having problems. This description isn't a lot to go on, but I would look to one of three main possibilities as the cause...
1. An undiagnosed medical problem.
2. A change in your cat's life.
3. Stress, such as a traumatic event or your cat's needs not being met.
Things to think about...
Has your cat been to the vet recently with this problem in mind and examined for urinary tract infections, kidney disease, and other conditions?
Many diseases and conditions can cause a cat to stop using the litter box and start using the carpet. In fact, since cats are good at hiding pain and discomfort, this may be the only obvious sign of illness.
If she were my cat, I'd call the vet and schedule a visit. If she hasn't been spayed, I'd discuss that with the vet as well.
Prior to the start of this problem, were there any changes (major or minor) in your cat's life?
This would include changes in the household, the family, schedules and routines, or changes to the litter or litter box.
Have any traumatic events occurred? Of course, the event may have happened when no one was around to witness it, but the question has to be raised.
This may include:
A scare of some kind (fireworks, thunder, some other loud noise).
Box guarding... another cat in the house attacking her near the litter box or preventing her from using it.
Additional things to try:
Increase the frequency of litter box cleaning.
Add an additional litter box to the house. After thoroughly cleaning the area, place the new litter box in the exact spot she's using. Once she's been using it for a while, slowly move the box each day towards its new home.
Increase playtime/exercise and mental stimulation to burn off stress.
Place a Feliway diffuser
in an area where your cat spends a lot of time.
I hope that helps, and please let us know how it goes.