HELP please - 11 week old dying - yellowish thin diarrhea

[countrysg]

This AM one of my girls is real lethargic and everyone else (6 others) are very worried about her (its so touching how they are so attached to each other) - no injuries - she won't eat (even blackberries) and she has yellow, watery diarrhea (which is totally new). Everyone else seems OK right now. I feed grow-mash that I mix some diatemacious earth into and I treat with some fruits etc as supplements. They also eat some pidgeon seed/mix. They also have a bowl of DE in their yard.
WHAT CAN I DO? Should I separate her from the others??

Thanks so much
Sharon

 

[chkn]

Did she eat something bad or maybe a parasite problem? This says something about yellowy poop:

http://www.chat.allotment.org.uk/index.php?topic=17568.0