She's way too skinny, and her comb is very small and pale. Both of these symptoms made me think Jackie has some other issue beyond her limp. I finally decided to deworm her, in case she has some sort of internal parasite that's messing with her ability to get nutrients. I guess lots of people deworm their chickens, although there are not many dewormers sold specifically for chickens.
I ended up getting some SafeGuard Canine Dewormer based on the success of someone else on the Backyard Chickens message boards. They sell it at Pet Co. It comes in three 1 gram doses, and I gave her a little less than one dose each day for 3 days. I made a little mash of the dewormer powder, a bit of her food and a touch of water. She ate it right down because I fed it to her first thing in the morning when she was hungry. Today was the last day of treatment.
As I said, she hasn't necessarily improved, but I guess it may take some time. One positive sign is that her poops are more solid than they were (sorry, I know that may be too much information). On the negative side, her poops are also green. Green poops can apparently sometimes mean they are not absorbing their food. (The green is bile.) So, I am hoping to see some nice, normal, light brown solid poops from Jackie soon.
If she continues to be sick, I am not sure what to do. Other possible fits for her symptoms are coccidiosis (treatable) or lymphoid leukosis (not treatable). At least, that's what I could put together using the Internet and The Chicken Health Handbook.
It could also be something like lice, which is weird, but I guess someone else on the message board had similar chicken problems and it ended up being lice. Anyway, we'll see... I really hope the dewormer did the trick.
Cross your fingers for Jackie!