So upset, newbie lost RIR yesterday, will someone help?

I am a first time chicken owner, raised 9 laying hens from day olds. They all lay about an egg a day (7 months old) and a few days ago this RIR wouldn't leave the nest box during the day, not that unusual, I figured she was laying and took the eggs from under her. She did not appear to be in any distress. I did notice she was wet underneath, my first thought was I stuck my hand in poop, but after smelling it (clear) it seemed to be eggwhite. That night when I locked them in she was still in the box, definitely NOT normal! I poked her and she was alive and ok. Then next morning I found her dead. I was sooooo shocked. She was fine up until then. All the other chickens are fine. Could she have been egg bound? I have never medicated or wormed these chickens and I do allow them to free range much of the time. I checked her all over and could find no blood, signs of injury, etc. I'm also concerned because we ate all the eggs from her.

One more thing...this past week I seemed to be getting some very small eggs, some with weak shells, but it has gotten much colder here lately....

Thank you so much for reading this long post... Dana