You don't say how old your dog is? In old dogs and puppies kennel cough can be life threatening and I would really not try and treat it myself.
A dog does not have to be in kennels to get it, it can get it walking down the street.
It tends to have alot of different symptoms in different dogs, I had three dogs and only one showed signs of a cough, and I only took one to the vet, the other two only had minor symptoms and were hardly affected by it.
This is one time when I would trust the vet, as if it is kennel cough he/she probably knows it is going around your area, and if your dog is showing such bad symptoms then she really does need treatment by a vet. I am sure your dog will be better soon if it is kennel cough.
I would be wary of giving her anything from the chemist if she is on medication from the vets as this could cause more problems.
There is a vaccine for kennel cough, you could ask your vet about it next time you visit.