Chickens do sneeze occasionally. Is she only sneezing, or wheezing from her lungs too? Occasional sneezing (not constantly) can be normal, but wheezing is another story.
I have a hen that seems to go on a sneezing bout from time-to-time. I watch my flock carefully - it's only her. Not sure why.
When it happens, I put vitamins in the water, which seems to do the trick. If that doesn't work, try isolating her and give her some antibiotics, but definitely try the vitamins first. Another soothing thing for her is VetRx (found at
Tractor Supply or a pet store). It's kind of like a Vicks VapoRub for chickens. It's a liquid and you can put it on their beaks, under their wings so their lungs open a bit.
I've learned it's common for chickens to have respitory illness sometimes, and wheezing can be a sign. It can be caused by bedding dust, not enough ventilation, mold, contact with other sick birds, etc.
What kind of bedding are you using? Do they have enough ventilation?
I'm sure the experts on here can give you more advice - I'm fairly new (9 mos newbie).
Hope this helps!