Quite often in people with a bad cough, an antitussive (anti cough) medication is actually avoided. The reason being, a cough clears the airway but if you were to stop the coughing, all that gunk in the lungs will just stay there and cause more trouble than if it were simply coughed out.
I guess there's not much else you can do except follow the vets instructions. Make sure her environment isn't too dusty - dust won't help the situation!
When I bestride him, I soar, I am a hawk: he trots the air; the earth sings when he touches it; the basest horn of his hoof is more musical than the pipe of Hermes. ~William Shakespeare