Back in Nov & Dec, my Luke cat did not always use his litter box. Sometimes he used the dog's newspapers instead. With him, it turned out that he was severely constipapted & he would try to bm but have great difficulty & discomfort. MAYBE he associated his pain with bm with the litter box. Now that his consitipation is corrected after several trips to vet, he is using litter box all the time.

So, is your cat having regular bm's or straining?

I also agree with others who suggested you take your cat to the vet for a checkup. Your cat probably is depressed but still I'd take her to the vet... Kay