Swollen tight belly?
That possibly could be ascites or fluid in the belly from heart failure, liver failure, or egg yolk peritonitis. Is she having labored breathing? Does it feel like fluid or firm like a tumor or egg material in the abdomen? I would seek a vet out if possible. Some people use an 18 gauge needle inserted into the lower belly to remove fluid periodically. Here is some info about ascites and EYP: