White watery diarrhea and limping (URGENT)

[zuzusplace]

I have a small free-range flock, as do my neighbors. There are approximately 24 birds in all and they are between 18 and 25 weeks old (varying breeds). We are in the US, and the birds have not been treated for anything outside of what the hatchery might have done. They are almost all laying pretty regularly at this point and are eating Layena crumbles. In the last two days one of the older Isa Browns has become ill. She has a watery white diarrhea that has completely caked her feathers (almost looks like pus from an infection only located around her cloaca). She is also limping (seems to have discomfort putting any weight on her right foot). She seems otherwise healthy, clean comb, no mucus from eyes or beak, no off-color spots on legs, etc. She's not breathing funny and her feathers look healthy, shiny, and not ruffled. We are not certain if she is laying right now since they all lay in the same place, but she does not appear to be egg bound. I'm at a loss as to what might be going on, but the neighbors have decided to put her down. Since it looks like there are some issues with other birds starting to develop cakey white stool I thought I better post before we lose the all. Also, in the more normal stool of the other birds, it is white with occasional pink spots (if that makes any difference).

Any help would be greatly appreciated.