Do you have an overly vigorous rooster?
I didn't think I did, but I have a young guy who was born this spring that has been trying out his skills and I wonder if her got to her. She is way smaller than him. The other thing I was thinking was that perhaps a hawk got her and started to take a bite when one of my roosters scared it off. We have a lot of hawks and since my Araucanas free range, they've been getting targeted the last couple of years. I lost two teenagers this year and two last year.