I have never had a female spray, however, she could be just doing it because the previously "marked" area is not cleaned properly. Cats have far better noses than people and they will return to a previously marked spot if there is a skerrick of odour left. Also if her previous owner had a baby, she may have felt "displaced" and then started to stress. Some people get a bit manic about babies and cats, so maybe she just didn't feel happy there. Let us know how it goes.