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Hello and thank you for requesting me. If she is rubbing her anus along the couch or the floor my concern would be the anal glands. Usually these get expressed with a bowel movement but sometimes if the stool is too soft they do not get expressed. The odor is pretty bad when they are broken open by the dog who scoots or rubs.
Some dogs just have anal gland problems regardless of stool. If this is the case it is best to talk to your vet if it is an ongoing problem.
Adding some pure canned pumpkin to the daily diet, 1 teaspoon , can firm up the stool and help with the glands.
I would try this first and see if you notice a difference. If the stool is already hard and there is still a problem then you need to see if the dog has problems with the glands.
Here is more on the anal glands.
(List of possible problems) http://www.vetinfo.com/dog-anal-gland.html