I would simply watch the droppings and the general well being of the others. You could also take in a fresh early morning sample containing both cecal and regular droppings from your other chickens to a local vet for a fecal float test, to look for cecal worms which are a precursor to...
A necropsy done by your state or regional vet on her body, would be the best way to get a diagnosis. Bright yellow droppings is not normal, and can sometimes be a sign of E.coli infection, egg yolk peritonitis, and rarely, blackhead disease or histmoniasis, which is a disease rare in chickens...