Ascites is not simply fluid most of the time, but a side affect of chronic infection/egg yolk peritonitis and/or internal laying or heart or liver failure, or even ovarian cancer. I just want people not to get the idea that ascites is simple fluid and that's all it is. Ascites is most often a symptom of congestive heart failure in broilers. In layers, it usually means a reproductive malfunction.
Of course, not trying to trivialise the condition but just wanted to provide a ray of hope. There is not necessarily a need to rush into euthanasia immediately on diagnosis, as hens can live with the symptoms (ascites fluid) for a long time with good quality of life. The underlying condition will probably cause death in the end but that may not be for a long time, and if the symptoms can be treated easily it just does not seem right to euthanise so early. Just my view and experience, but maybe i have been lucky. My hen with chronic ascites had an acute illness recently and i had to face the prospect of her probable death or my difficult decision to euthanise. Luckily she pulled through with some baytril. For now anyway. In cases of incurable disease each owner has to make their own decision.
I hope it turns out ok for the OP's hen.