I am so sorry for your loss
Yesterday I lost my favorite sweetest girl to internal laying.
I couldn't find a vet who would treat her for this, and was afraid to try to "treat" her myself as I have never dressed/cleaned a bird and was terrified that I would remove the wrong parts, though I did consider it many times out of desperation.
Once they start laying internally they will always have this problem unless they get a chicken hyseterectomy. basically what you saw was the yolk that cooked in her body. I guess this (internal laying) can be common in production breeds/ hens that are prolific layers esp as they get older. I hadn't heard of it before a couple weeks ago, when I discovered she was not well.
In any case, she seemed to be hanging in there until yesterday she seemed to be suffering so we decided we would cull her now, but by the time I had gotten back from the hardware store with the supplies she had already passed. It was relief for me that she passed on her own as I have just been sick over the thought of having to do it (hoping some way to save her would present itself), but I also didnt want her to suffer.
I just adopted her and her sister early spring and they are just over 3 years old. They are my first hens. I am very sad.
BUT I have learned an amazing amount of info here from lots of generous, kind, people. So I just wanted to say I'm sorry and welcome to BYC.
Maybe our girls will keep each other company in chicken heaven