I'm very sorry. At 4 years old, with a mass in her belly, it's likely that she has a reproductive problem. The mass could be infectious material from salpingitis or internal laying, cancer, or fluid from a leaking liver (which is a symptom of something else). If it's fluid (ascites) that can sometimes be drained which can make them more comfortable for a time. But it will recur as the underlying condition is still there. And there is some risk in draining, if too much is drained too quickly it can result in shock, which can be fatal. With most of the reproductive issues, regardless which, crop problems will often also develop. Their digestion can slow, or stop completely, resulting in crop stasis and souring sometimes. Sadly, reproductive problems in hens over the age of two are not uncommon. Sometimes imaging can show what is going on, but sometimes it doesn't. And cost and access are problems for many people. And the majority of the time there really aren't good treatment options that will change the outcome. It might buy them some time, but won't be a cure. When I have a hen that presents like this, I no longer treat, I just provide supportive care. When they go off food and water, isolate themselves, or are attacked by flockmates, I euthanize rather than let them suffer. If you want to know for sure, then necropsy is the best way to know. Many state labs are reasonable and can provide answers, and sometimes peace of mind. Link below to state labs, you can contact your nearest for particulars.
https://www.metzerfarms.com/poultry-labs.html
