Kennel cough is best left to heal on its own, but your vet can prescribe antibiotics if it is really severe. As for your GSD, many dogs have a very high prey drive. My Greyhound could never be left alone cats because she would rather kill them than live under the same roof as one. As one owner said, "Some dogs like cats, while other dogs like CAT."
Since it seems like your animals are having such conflict, I wonder if the best thing to do is give the dog or cat up. If you can't do this, then you MUST muzzle or crate your GSD whenever the cat is in her presence. To sort of de-sensitize the cat to the GSD, you can put Kacey in a crate and hold your cat a few feet away. Pet your cat and reassure it. If it's uncomfortable, let go of it and try to repeat this again and again until the cat tolerates being close to the GSD. If Kacey shows any excitement, like perked up ears and whining, she's probably doing so because she wants to attack the cat. I would reward good behavior, like relaxed ears and ignoring the kitty, but either reprimand or ignore bad behaviors like perked ears and excited whining.