I have a hen who seems to have abit of a sneezing fit everytime I stir the bedding. I have allergies so I sneeze also, I know that is irratating. I usually spray it down with a light spritz of vinegar water before I stir it up now and it helps alot. so your hen gets along ok and everything? Wow 5 years of sneezing.... I know that this time of year they can get runny noses and have been told by the vet in town that sometimes that is just a bodies way of expelling the unwanted pollen and other fall residue in the air. Hopefully that is all it is in this case.Allow me to interrupt your argument to address the sneezing issue the OP asked about, please.
Sneezing in absence of any other symptoms is usually just caused by something environmental. Don't go to the worst case scenario right off the bat. I have one hen who is six years old and has sneezed every day for the last five years. She has small nares and I suspect malformed sinuses as her head seems too small for her body (hatchery Brahma). She is not ill, but she is very sensitive to every little thing.
Check ammonia levels in the bedding at their level-you may not think it smells, but get down at hen height, stir it around and take a big whiff. Check for dusty feed, mold growing in the coop, etc, before you jump to any worse conclusion about illness in a bird whose only symptom is sneezing. Even new plywood and caulk can cause irritation and sneezing fits.