Once a cat goes into heat or estrus, she may stay in heat for several days, to 2-3 weeks. Some cats, once they are sexually mature and enter estrus, do not come out of heat unless and until they are either bred to a full male cat, or spayed. The majority of cats will cycle in and out of estrus during the prime breeding season (roughly December through August), returning back into heat approximately every other week.
She may be trying to leave her scent around for the males.
