my chicken is sneezing

[chicksn2pigs]

Please help
I have a small mixed flock and one 4 year old chicken has started sneezing.
She is showing no other signs of ill health, no mucus or discharge around the beak or eyes; good colour comb and wattle; eating well; feathers, vent, etc all looking good.
I know I'm supposed to separate a sick chicken but is she sick? Could she just be sneezing or does it have to be a respiratory disease?
I put apple cider vinegar in their water, use wood shavings for bedding and they free range in the garden. Does anyone have any suggestions?

 

[lilchick06]

My chicken sneezes occasionally and nothing has ever really happened. I do notice they sneeze if they are eating something powdery, like when some of their food is in a powder. (The powdery food at the bottom of the bag) But if dirt or sand or anything like that gets on their beaks, they will usually sneeze. It's probably nothing to be worried about though.