Ah, poor BG. Kennel Cough sounds so horrible. When my Bella came to me she had kennel cough that she got immediately AFTER receiving the vaccine (through the rescue). I never vaxed her for it ever - especially knowing she had had a reaction (not that I vax anyway). I bet Scarlett picked it up at doggy school from a recently vaxed dog. Bordetella (as well as Pertussis - its namesake in humans) is known to shed. This is why most kennels won't allow a dog into care unless they are vaxed AND it has been at least 2 weeks from vaccination. It's a self-perpetuating process......vax dogs so they shed so other dogs get it and then vets and pharma can use statistics from all the dogs that "got kennel cough" to prove the vaccine is needed.
I hope BG is feeling better soon!