Some threads on the topic:
https://www.backyardchickens.com/t/639749/timeline-of-internal-laying-update
https://www.backyardchickens.com/t/748821/internally-laying-update-death-by-rubber-egg-graphic-pics...
My first girl I lost was about 6-8 months old I think. Under a year. She never laid an egg that I know of. I was new to chickens and didn't think twice about how easy she was to pick out because of her tiny comb. She went from apparently fine to dead in less than 3 days. I had only had her...
Looks to me like internal laying. Based on my experiences with it, I have not doubt in my mind. I only had one hen who died from it poop yellow like this. I doubt it's blackhead.
The antibiotics were working because her illness is probably due to the yolk buildup in her abdomen becoming...
I've lost a few hens over the years. All were factory birds, all died of internal laying. Some of them I didn't know it was IL until after they died (if the smell of rotten boiled eggs at time of death isn't enough to tell you...). Some lingered for months, flirting with the infection, laying...