Hi, thanks for remembering!
I never got anything close to a diagnosis on Jezebel. I wrote to many veterinary professors at various universities and included photos, but most declined a guess, saying they needed to see the chicken in person. One did guess that it was some type of lymphoma, possibly developed due to an injury like pecking. He said there was no treatment and I could cull, but that there is always the chance it could go away on its own. I messaged several Buckeye groups with no response. I did email back and forth with a guy on Reddit in the backyard chicken forum. He said that he had a chicken with a lymphoma on its abdomen and was able to give the chicken a form of medicinal cannabis oil (the medicinal part without the high) and saw a reduction in the size of the lump. However, I am not able to get that type of thing. A friend made me a blend of some cannabis with coconut oil - to try as a topical salve. Needless to say that did not work. :-(
In the summer, I saw several bouts of backward walking from Jezebel. Just a few steps - but it seemed almost involuntary. I worried that it was affecting her nervous system. Since then, she has actually worked her way up a few places in the pecking order and she seems active and normal otherwise. She really is a great chicken. If I had more room I would definitely get another Buckeye.
Thanks for checking in!
Here are some recent photos...