Is kennel cough contagious

I say yes! My 4 shelties are strictly indoor dogs with the exception of using the bathroom in our fenced in very small, & clean yard. We fostered a stray feral cat and her kittens for 2+ mos in order for them to become adoptable.(totally isolated from our dogs) Last month we surrendered them to the humane society and since have made 2 visits there. My 6 yr old MUST pet every dog she sees. My 9 yr old, otherwise perfectly healty dog has come down with kennel cough. We do not go to dog parks or any other parks with her. They are NEVER around any other animals, ever. So the ONLY thing that makes sense is that she got it from US who got it from the Humane society. I was told a dog that had it can spread it for up to 3 wks AFTER they stop showing all signs of having had it. SO this is why I am saying absolutely yes!