Found one of my younger hens dead in the coop today. Ascites (aka Water Belly). She was running around just fine yesterday. I thought when they got it, they tend to get a bit lethargic, lay around, or be less active, and have possible respiratory issues. She didn't. She was out running around just like the other one. I'm positive of my diagnosis. I double checked all the others just to make sure there isn't something else going on too. Nope, they're all fine. Even the old gals are spunky, laying, and doing fine.

I am sorry you lost one!
chickens are prey and try to keep up the look of health until the end. If you see one looking sick, it is very sick.
The rest are likely fine