Usually the dark purple comb and face means respiratory and/or heart failure. The strange bruising on the neck and crop that came and went I'm wondering if it was some type of bleed or blockage so that circulation to that region was cut off maybe resulting in tissue death and systemic infection. Maybe the bacteria was inside the crop, I don't know, but it seems there was some crop involvement and that the crop didn't appear to be functioning. She was a big, healthy hen, maybe she didn't have a good enough ticker to support her size. Anyway, I'm so sorry. These cases are always the hardest when you have a big healthy bird and they get taken down like this. I'm not sure there was anything you could do or even a vet could do. Some type of injectable antibiotic (I don't know, Tylan?) may have helped but if there's tissue death it wouldn't have saved her. I'm stumped she took such a sudden turn for the worst. I'm very sorry for your loss. Did she have any type of bite marks anywhere in the crop area or where the bruising came and went?