One of my Old English (at least that's what the woman who sold them to us said they were) was acting sickly yesterday. She was off on her own from the rest of the girls and had her head pulled down to her chest. She didn't even perk up when I went to give them their rainy day oatmeal. I went out this morning and noticed she wasn't in the run and I knew. Opened the coop up and she was dead in front of the nesting boxes. She was lying on her stomach, wings out, eyes closed and beak slightly open. She had been fine up until about 2 days ago, but yesterday she was really bad. Any thoughts on what could have happened?