Just like male cats, female cats do spray. They do so for a number of reasons, primarily to advertise their reproductive availability in hopes of attracting a mate. Spraying is a normal instinctive behavior for an unspayed female cat.
Female cats may spray for a number of other reasons, such as stress caused by the addition of a new cat in the home, a difference in routine, a new home or a lack of adequate attention. The key to stopping your female cat from spraying is to get her spayed and determine the issue that is making her spray. Once you have determined the exact cause, you can then try to reduce the cat's stress.