Is she ok?

I suspect the horse has heaves and that you may have some bad hay. Heaves is an allergic response to molds and causes inflammation in the airway which must be treated with prednisolone or dexamethasone. Any breathing problem, and especially a breathing problem when the horse is at rest, is good cause to call the vet out. Exposure to molds in the bedding or barn environment can cause heaves but the most common cause is hay which has molded after being baled with too high of a moisture content. You should call the vet out to check the horse and if it is heaves you should locate the mold source and eliminate it.