Why is my bielefelder sneezing

[AmeraucanaHank]

I have a year old beilefelder hen, yesterday and today she has been sneezing. why!?!

 

[Wyorp Rock]

How old?
How often?

Have you looked to see if her nostrils are clogged up? Anything inside her beak (canker, lesions, mucous)? Is she sneezing when she's been eating/drinking/dust bathing? Crop emptying overnight? How much ventilation in the coop (any strong ammonia odor, mold)?
Have you brought in new birds?

There's dozens of reasons why a chicken can sneeze - a little more info and some photos may be helpful.