She may have had a genetic issue. Last year when we first got our pullets (they were about 13 weeks old), they all seemed healthy and fine, and then a few weeks later one of them (a blue cochin) was just standing around. We noticed she was extremely skinny, but had a full crop. I freaked out and took her to an animal hospital, saw an avian specialist, and $700 later we came home without a chicken. They euthanized her because after running tests on her and doing an xray, they noticed that (and forgive me for not remembering exactly what they said) at a particular spot somewhere in the whole digestion process which I cant remember, she had too narrow of an opening for food to get through. Some food must have been getting through though because she managed to live for about 16 weeks. They said she hadnt eaten anything that a chicken couldnt handle...they saw grit and chicken food, and they said it most likely was just the way she was born. I'm sorry for your loss.