That is sad. I'm sure she is very lonely without her buddies.
I found this, since you asked how she could have caught it. There is quite a bit of info there, so you can read it all at the link.
How Did My Dog Catch Kennel Cough?
Dogs can catch kennel cough in several ways. It can spread through aerosols in the air, directly from dog to dog, or through germs on contaminated objects. Kennel cough is often spread in enclosed areas with poor air circulation—while boarding in a kennel or an animal shelter, for example, or through direct contact while sitting in a vaccination clinic, training class or dog-grooming facility.
Kennel cough is so contagious that your pet might even catch it from sharing a water dish at the dog park or by simply greeting another dog. Most kennels will not board your pet without proof of a recent vaccination against parainfluenza and bordetella, two of the main causes of kennel cough.
ASPCA | Kennel Cough