Sneezing is not a symptom of gapeworm, but that along with sneezing are signs of a respiratory disease. Infectious bronchitis or IB, mycoplasma or MG, coryza, ILT, and aspergillosis are common ones. Mold from wet conditions can cause aspergillosis. If she is active, alert, eating and drinking, she doesn't sound too sick. I would be cautious using DE, since it is irritating to lungs and can cause breathing problems. Make sure that you always have good overhead ventilation, limit dust in feed or bedding, keep the temperature cool with a fan in hot weather, and prevent wet or moldy conditions to decrease chances of respiratory diseases.
Edited by Eggcessive - 5/4/16 at 5:48pm