We picked up 5 pullets on Friday, everything looked okay on Saturday and Sunday, but Monday morning the 10-week old Buff Orphington was a little slow and lethargic, this got worse throughout the day (in hindsight she also didn't eat much yesterday). She was puffed up and antisocial most of the evening. This morning when I went to let them out of the coop, she wouldn't leave the nesting box. She was shaking and puffed up. I checked for lice and other parasites and didn't see any obvious signs of either. The other 4 chickens seems to be settling in and have not exhibited any of these symptoms. What could it be?