Dog might have heart worms

Elizabeth • Mama to B: 6/23/11 B: 5/10/13 G: 3/1/16 B: 10/26/18
My dog is a 14lb mutt. She is 13 years old and has been coughing bad. The vet thinks she might have heart worms. I find out Monday. She is in good health other than the cough that goes on ALL NIGHT LONG. I'm worried about doing treatment. I know it is also very expensive. Anyone have advice or experience with heart worm treatment on an OLDER dog?