I can't remember which it is but it seems like ascites is caused by excess protein or salt. Protein I think. I'm not sure, might be other causes too. Those birds are really hot inside when they have ascites. I guess that might be a fever. Wish I knew what to tell you to do. I've seen it quite a bit in CX meat birds so I'm thinking it is excess protein. Good luck with your hen.
Ascites is a symptom of liver failure. My boyfriend suffered ascites while he was waiting for his liver transplant. He says having ascites (fluid buildup) is VERY uncomfortable. The actual draining with needles is painful to say the least (Mike's description). He does admit he felt better after the procedure.