I'm so sorry you lost her. I also had a similar experience, and lost a hen quite suddenly. She was fine at 4:30PM but by 5:30PM when I went to lock up the coop, I found her in a corner of the run all hunched down. I took her inside and she passed away about an hour or so later. That happened about 3 weeks ago and none other of my flock have gotten ill. I suspect she ate something poisonous, because it overtook her so quickly.
I am sorry for your loss
Penny
I am sorry for your loss

Penny