Whenever a cat begins sleeping in the litter box or spends an inordinate amount of time there, have her health checked by the veterinarian. Urinary tract disorders can sometimes make the cat feel the urge to "go" very frequently so she just gives up and stays in the box.
If she gets a clean bill of health, it may be that your kitty has decided to "guard" your other cats' box in a power play. But more likely, your
cat is just sleeping in the litter box because she likes napping in an enclosed place - and because it smells like her and it makes her feel safe. Try giving her a better place to sleep. It doesn't have to be a fancy bed. In fact, if she likes that litter box so much, why not offer a similar box just for sleeping?
Oftentimes, shelters provide their kitties with shoeboxes and the cats become accustomed to
snuggling in these containers, so if your cat was recently adopted from a shelter, the litter box may feel familiar to her. In that case, once she gains confidence in her new home, your cat's sleeping behavior may change.
