Ah, I'm glad you had some success in identifying some of the abnormalities that could lead to a diagnosis. The lack of eating and drinking certainly pointed to something significant. I'm sorry you lost a new girl before you had time to enjoy her, that always makes a responsible owner feel pretty...
I came here to comment on her fat levels too. That much yellow fat is a lot for a backyard chicken. If you are concerned about Marecks I believe you can look for major nerves and see if there are any lesions present along the nerve tracts. My dissection skills are more along the lines of humans...