Welcome to Websleuths.
It was the media who reported the trauma to the dog initially. As others have pointed out, perhaps the tumors/water combination caused the dog to appear that way on a cursory first sighting. What I am wondering is why her things were left in the car, wallet, etc. It sounds like she just planned on running in and grabbing whatever it was that she wanted and/or needed and return to her car? Or is that something everyone does anyway in the community?
Did Robin have a pretty fixed route she would walk Bella?
ETA: Was the dog found with her collar on and leash attached?