Possible Marek's bird, organ question thanks!

So I had an awesome Russian Orloff about 10 months. A couple of months ago she started laying, but began to act lazy and seemed to to be loosing her appetite. But I always gave her walnuts when I'd see her. I noticed she may have been losing weight, but I wasn't sure what to think as it has been very cold lately and she insists on roosting in a tree alone, and has very thick feathers. Saturday my bro found her on her side in the snow. Eyes alert, but the right half of her body paralyzed. So was the left, but she could just barely flap it, and the left leg could just barely move. I did some some research and thought it might be Marek's and brought her in. She would not eat so I fed cayenne and a few other liquids in a dropper.
Her condition continued to deteriorate. She put her head down, was breathing heavier, then left her beak open when resting. The eyes seemed normal. Her poop was normal color and did not smell bad. On Monday only liquid came out of her, it was mostly clearish fluid, that had a funny smell. Monday night she passed. I am a newbie to chickens, probably shouldn't of let her suffer so long, but I had hope. So I thought I would do an autopsy on my first chicken, and at least feed her to my dog.
So we got to gutting, and I only remembered vaguely that some people cut around their bums or something. Now after seeing her defeathered, I don't think she had an ounce of fat left anywhere. But her lower stomach was very soft and full. The skin by the bum was very thin and I punctured some large mass. Took it out and left it drain some rather "fowl" smelling brownish liquid. Like a cup at least came out. Took this mass out of a skin encasing, don't know if if was the liver or kidney. Smelled bad, cut it open, there was stronger smell inside it with some tan discoloring in the dark red organ. Now I don't know what this organ is, but it was the size of a soft ball, no joke!! I don't think its supposed to be that big. Like the mass was most of her insides!
I was reading up on Mareks and heard it can enlarge - either the liver or kidney quite a bit. Also the bird is vaccinated against Marek's. Also noticed a bit of what I think is called "Alambama Red Leg." She, and my other chickens have all had this marking since young. None of my other chickens seem the least bit ill though.
Any insight or ideas?