That could be a pecking injury or it might have been a hernia. It can be common for flies to lay eggs there which turn into maggots and fly strike, so look for any or be aware. Keep it clean and apply some Neosporin ointment there twice a day.
The severe outbreak dosage of Corid is 2 tsp of the...
Corid is pretty harmless to use even if it is not coccidiosis. If you have a regular dog vet, and your dog or cat needs a vaccination, ask if they will do a fecal float. Poop pictures are welcome if you haven’t posted one already.
At 5 years old and not laying for 2 years, I would think it might be a reproductive issue or possibly cancer. Has there been any rat poison that she could have gotten into? Can you see a vet? I am not going to be online much for a few days.