Welcome to BYC. Is your hen’s lower abdomen enlarged and full, firm, squishy or tight? Water belly (ascites) is due to liver problems and it causes the liver to leak bile and fluid into the abdomen. Several common conditions can cause this including coelomitis (egg yolk peritonitis,) salpingitis, which is early coelomitis, fatty liver disease, cancer, and sometimes heart failure. All of those conditions are incurable, but she could live awhile with it. I have suspected hens of having this by the enlarged lower belly under the vent and yellow urates in their droppings. Normally the urates are white caps. I have only drained one of mine with ascites because she had labored breathing, but she died within 2 weeks at the age of 11.