I’m sorry about your dear hen. My money is on a reproductive disorder. I base that guess on the combination of:
• bloated abdomen
• wasted breast muscle
• lack of eggs
• lack of appetite
Is an avian vet an option? You might want that fluid tapped to see what color it is. A vet can also palpate the abdomen to feel for masses.
I recently had a hen with similar symptoms. The avian vet was unable to access the fluid; it seemed to be behind a mass. I treated her aggressively with enrofloxacin and ibuprofen, plus some aloe detox. Then I asked the vet for a hormone implant to shut down her reproductive tract. Thankfully, my sweet girl responded to the treatment beautifully. Of course, there is no guarantee it would help your hen, especially if there is something like cancer going on. Depending on whether she is a beloved pet or not, it’s something you might consider.
Can we see a photo of her body language? Is she drooping her tail or wings? Walking like a penguin? Panting? Any other visible signs of illness?