There are a few threads here on using sand in coops and runs. The peeps here are divided more fiercely than the North and South was during the Revolutionary war. I am in favor of sand just for the record. First, ,, what type of sand are you using ??? Here are some thoughts, views, and opinion, on using sand. Use course sand if at all possible. Construction sand is fine as long as it is the one for concrete use. Masonry sand is finer, and tuck-pointing sand is like powdered sugar. Avoid these 2 finer sands.
I think your chicken will recover from this breathing ailment, on her own. I truly don't know of anything you can do to remedy her condition, other than keep her away from the sand.
The finer the sand, the more dust prone. Dust is not good for anyone as well as chickens. JFYI.... construction sand is supposed to be washed. That means that the finer particles should have been washed out in the process. NO PROCESS IS 100% PERFECT.
WISHING YOU BEST