If this is not something Fluffball has done previously.....I would be a little concerned at least. If she is stained on her back legs, that means that this is not the first time. Incontenance can have several causes..... hormonal issues, urinary tract infection, bladder sludge, stones....even an early presentation of EC. If I were to make an error in judgement, I would make the error on the side of caution and seek the advice of a qualified vet. This might require some diagnostics such as blood chemistries, urinalysis or x-rays. A CBC with EC titer would be something to consider. In the meantime.....make sure she is well hydrated. And try to monitor urine output as much as possible.
Randy