If it's egg yolk peritonitis from egg bits floating in the abdominal cavity, they need to be surgically removed. I was quoted $1000 for that surgery. Then one can do the implant.
-Kathy
If her belly feels like it's full of fluid you could try draining her. Some need to be drained every few day like eggcessive said, but others might only need it once every six months, just depends on the hen and what the cause of the fluid build-up is.
This is how I do mine. The hen pictured...