“When I first reported it to the surgeon who did her surgery, she said it was just a side affect of the medication, but now almost two months have gone by”.
Give the surgeon another call. It could be a senior dog thing. Their anal sphincters don’t work as well. If he isn’t helpful, I would ask him to refer you to someone who can be.
Or, see what her regular veterinarian thinks. There a a few reasons that this could be happening….only a veterinarian who has examined your pet can give you an educated guess.
Are you feeding her too much?
PS: No free feeding.
