Sorry for your loss. It sounds like she could have died of Mareks disease. A necropsy by the state vet is the best way to get a diagnosis. If you have another chicken with similar symptoms, I would get a necropsy by contacting the vet on this list for your state...
Instead of NutriDrench which does not have riboflavin, I would use 1/2 tablet of human B complex daily. It could be a riboflavin deficiency, but sometimes Mareks disease could be the problem.