Get Your Dog Care Questions Answered by Experts
If she has been boarded at a kennel recently, it could be kennel cough, a common respiratory illness that is highly contagious. Even if animals have been vaccinated, they will still get it if they are exposed.
Aside from that, tracheal problems and heart problems can also cause coughing, as can a general virus.
Any time that I hear of an older dog coughing, I immediately think of a heart problem, especially if the dog is not on heartworm prevention.
You should be pretty concerned. I think that you should make an appointment with your vet as soon as you are able.
Let me know if you need more details or do not understand.