Erm, ND is also on that list. Could be a strain attacking the nervous system. I suppose diarrhea only happens with NDV strains attacking the digestive system. Might have been a secondary infection or just something she ate.
500ft is pretty close. Not sure if dried dust from droppings can fly...
Walking backward is a sign of neurological issues. Vitamin E/Selenium deficiency is one reason, but there are other possible causes if you think the diet is in check. If she sneezes and has diarrhea, I would think of coryza. Here is a list of more reasons why a chicken walks backward, including...