I don't know if that is common, but I would take her to the vet sooner rather than later in case she has pyometra. Can you tell if she has been running a fever? Any purulent discharge from the vulva? Look up pyometra because it is life threatening if she does have it. That is about all I know of unspayed females, but I understand it is much more common than many people think. The reason I thought of this is because many times bowel habits will change when they are sick. Good luck & post updates when you can!
Pyometra | AKC Canine Health Foundation