She wasnt in a cageshe was in a coop she really enjoyed.
Sometimes it just happens and nobody knows why. A couple years ago, my best 2 yo. RIR rooster came out of his coop, crowed once and immediately dropped over dead. Never sent him in for autopsy because it was a holiday weekend. Someone I knew had a draft horse that did the same thing.
I'm really sorry for your loss. She was a beautiful bird.
