I have a month-old pullet who got sick a week ago. First it was general lethargy. I was out of town so I asked my nephew, who was watching the chickens, to give vitamins and electrolytes. When I got home three days later, I discovered she was crawling with little red mites. None of my 19 other chickens has a single mite that I can find, but I treated everyone. Mites seemed to go away. She also had brown crust at her ears. I cleaned it off, applied peroxide, which bubbled like crazy. Yesterday, her head seemed to be swelling behind her ears. I saw a tiny wound like a pimple near her beak. I cleaned and applied blu-kote to it and started her on antibiotics. Then I saw that she had a large gumball-sized bubble under her skin near her wing, like an air pocket. After various online research I inserted a needle and tried to drain the air, but nothing came out, so I figured I was doing it wrong and stopped. She died this morning. What the heck happened to her?? Is it contagious?? No other chickens are showing signs of illness. Do I need to do anything?