I'm so sorry for your loss, it is so hard to love these sweet birds that can't tell us what is wrong. I am certain she knew she was loved and lived a wonderful life. <3
Hugs to you, you have done an amazing job being a chicken momma to have an 11 year old chicken. You clearly love them and I think most importantly, giving her love and the necessities to keep her comfortable are the best things you can do for her.