How tragic to loose one of your girls, nothing brings your heart back from the loss. You will love your other biddies and treasure memories, yet preditors are a constant challenge with all of us. You can build, wire, and secure everything and often its not enough. We did not have chickens, geese or ducks for years due to the heart ache of these preditors that come in for food.
Maine has just been blessed with opposums and I'm not sure how to deal with them, what they eat and if they like chicken. That is a bit to close for comfort.
Take care of yourself and there is nothing to blame except that nature can be cruel.