I'm so sorry. With this development, it's highly likely that she got into some anaerobic bacteria, and I've had it kill a chicken of mine in 24 hours of the first symptoms.
Two things I recommend. Watch all your chickens for signs of illness that this hen had, and start them immediately on amoxicillin if you see symptoms. The second is to block off access to the compost pile until you can clean it out and expose the bottom layers to strong sunlight to kill botulism toxin that is likely lurking in that soil.