Sorry about the diagnosis. Let us lnow what happens. If you should lose her you state vet in Trenton could perform a necropsy to see what was wrong. Here is a link for that:
https://www.metzerfarms.com/PoultryLabs.cfm
She may feel more comfortable if she is separated, but next to the other chickens. A dog crate with food and water is good for that. You can move it in and outside.
Many hens suffer from lash eggs inside them, and many times we don’t even know they are there unless whe perform a necropsy after death. Here is a photo in post 42 of a hen with ascites being drained:
https://www.backyardchickens.com/threads/laying-hens-with-water-belly-or-ascites.68731/page-5
Thanks for the xray, but I am not very good at interpreting a chicken xray. Is her lower belly under the vent enlarged and swollen, spongy or tight like a drum? She could be suffering from ascites or water belly, which could make her breathing more labored. A mass could be from lash egg...