Aversion to the litterbox. This means that your cat has decided that the litterbox is an unpleasant place to be. This kind of an aversion may require you to completely replace the litterbox so it no longer reminds your cat of unpleasant experiences. You may need to buy a new box, put it in a new location and use a different type of litter. Remember to keep the box clean - scoop out stools and urine every day, and wash the box and completely change litter anywhere from every three days to once a week.
All animals develop preferences for where they like to eliminate.
These preferences may be established early in life, but they may also change overnight for reasons that we don't always understand. If your cat often reaches out and scratches the carpet after she uses the box, she may come to prefer to use carpet instead of the litterbox. Many cats seem to develop a preference for either soft surfaces such as piles of clothes or the bed, while others may prefer slick surfaces such as the bathtub or the kitchen sink. Cats with an outdoor history may prefer dirt or grass. To resolve a surface preference problem, the material in the litterbox needs to be made more like the textures your cat prefers for elimination, and the places she's soiling need to be made less attractive.