Crud, Shade has a cough

I rode her yesterday and she was going along feeling strong we had gone about 3 miles with a fair amount of trotting after a good warmup, and we canted up a little rise and she coughed. I rode a bit farther thinking the cough was just clearing crud/dust out, but she started coughing more, so we walked home. In fact I led her most of the way because the cough starting sounding so nasty. Every 1/4 to 1/2 mile. COUGH COUGH with head stretched out to make her airway as straight as possible, and then swallowing what she brought up. My poor sweet mare. I'm waiting for my vet to call me back. I need to ph home and see if they called there and set an appt and gave any instructions.