What is wrong with my goldfish?

It is about 6-8 inches long and I thought she was ready to spawn a few months ago. (the other fish and her were chasing as well as her abdomen was enlarged) He abdomen just kept getting larger and now it is about the size of a base ball. One side is noticeably larger. Her appetite is good, but it is starting to affect her swimming. PS..........I paid a quarter for this fish 3 years ago, I am not going to the vet with her.