Last night, my favorite chicken, Duck Duck, was standing in the corner of the run looking droopy. I picked her up, put her in the coop and offered her some mealworms. She turned her head away. Her vent looked good, no signs of egg binding on palpation, and she had just laid the day before, none if the birds have mites, no runny eyes or nose, no sneezing. No trouble standing. Wattles and comb looked normal. The day before, she was 100%. I went inside to set up a sickbay and formulate a plan if action involving warmth, vitamins, vetrx, and good foods. By the time all was ready, it was a few hours past dark and I didn't want to disturb her sleep and decided to wait til morning to bring her in. Well, 5 am I went out to the coop and she was dead. Nestled in the straw, face down like she fell asleep. Aside from our family's great sadness at her loss, I'm also confused about what caused this. I carefully checked through the coop and chicken yard for anything dangerous she may have come in contact with, or any unusual poop...nothing.
Any ideas what could have caused her very premature death?