We ordered 8 baby chicks from mypetchicken.com last week. They all arrived alive and have been eating and drinking normally. We woke up this morning and our only lavender orpington was dead. She was fine the night before. She had no apparent symptoms or indication that she was dying. She appeared healthy. She was one week old today. All of my chicks were vaccinated for Mareks disease and I didn't notice any signs of coccidiosis in their stool. The other 7 chicks are acting fine, but so was this one before she died. What could be the cause?