Sorry for your loss. It sounds like she was molting and it could have had to do with that. But if you didn't see any external injuries or other abnormalities, it's very hard to tell without doing a necropsy.
He's gorgeous. I have an affinity for white chickens.
I have a question - How do you keep your roosters from getting major frostbite in the winter? It's my first winter with a rooster and he has a large single comb.
If your coop doesn't have a dirt floor you're better off doing the deep bedding method (no moisture) and keeping it dry. Dry poop = fewer pests and a lot less mess. In the run, the litter will break down into the ground eventually, but it may be slower if you have a roof on the run or the...
How wet? If it's just damp when it rains or snows and they have a large, very dry coop to retreat to I wouldn't worry about it. If it's a swamp then you need to do something.
No, diatomaceous earth should not be fed to them. It is a respiratory irritant, especially for animals with sensitive respiratory systems like birds. Crushed or flaked oyster shell is what they need.
I love PVC sheets on the wall. I have this kind in my duck coop: https://www.homedepot.com/p/Veranda-1-4-in-x-24-in-x-4-ft-White-Reversible-PVC-Trim-Sheet-H060XWS6/312995340
https://www.homedepot.com/p/1-4-in-x-48-in-x-8-ft-White-Reversible-PVC-Sheet-H060AWS3/309355877
It's easy to install...
:welcome You've come to the right place! There are so many great people here and loads of useful information about all kinds of animals, not just chickens! Feel free to join in any of the threads and have fun!