There is no treatment for ascites, when I have a hen develop that I have her put down as it usually is a slow and unpleasant way to go. If your hen has that much of her lower body swollen it sounds like that's what she has. She has likely stopped laying because of whatever is going on with her that is causing the ascites, not because she is egg bound.
As I mentioned before, some people do drain these birds but that does not cure whatever problem is causing the ascites, it only makes the hen more comfortable for a short time. The fluid always returns. There is some underlying reason this is happening and none of the possible causes are anything that will have a good outcome.
As a side note: If you decide to try to force feed this hen with a turkey baster as was mentioned, be VERY careful. (I personally would not recommend it) It is very easy for chickens to aspirate food or fluids into their lungs when force fed in this way.