Question

I took my jack russel ,Kira, in to see the vet a week ago 2-11-09 because for a day and a half she had been coughing and it was steadly getting worse. It sounded like what kennel cough was said to sound like. A almost honking sound with a gag on the end. The vet checked her over and said that her lungs were clear and it seemed as if she had a upper respirtory infection. maybe she had inhaled somthing. He gave me Torbutrol 1mg for cough control and Amoxicillin 100mg for infection. I was told also that if it had been kennel cough my other two dogs would of had symptoms by now. By the way my dogs are never out with other dogs that I do not know the dog and the owner and are sure are healthy. they also are up to date on all there shots. Kira slowly started getting better even though when excited she does cough still. I'm now worried about my 9 month old labadoddle she started coughing and gagging today. What could this be? what do I do ? and how infectious is this possibly?