Im so very sorry. Dont feel you did anything wrong, you did more for her than most people would have. You have made very wise decisions, and unfortunately this last decision I think your dog would agree is also a very wise one.
Im sorry you had to experience a pyometera, I think too many people think they are an easy fix but frequently they are not. Vast amounts of infection in the body do take their toll, especially on these older creatures. She was a tough dog to hang in there this long, but at the same time I bet she enjoyed your home cooking
You gave her the best chance possible and sounds like she lived a very fulfilling life Hugs to you and shade.