Kennel cough is not necessarily an emergency, if the dog is just coughing and snotting, but is still eating and drinking. Many healthy dogs fight it off without antibiotics -- essentially like a common cold.
You can probably just wait to go to the vet on Monday -- let them know you suspect KC, and they may ask you to use a side entrance to keep your dog away from other dogs because KC is HIGHLY contagious.
KC can become
an emergency if the dog can't fight it off -- GSDs with weakened immune systems can crash very, very quickly. They stop eating and drinking, and they become very lethargic. At that point, they really need to get antibiotics quickly (usually doxycycline). There's a serious risk of pneumonia when they crash like this. For this reason, my preference is usually to start a GSD with KC on a round of antibiotics, to prevent a "crash."
In the meantime, eucalypus essential oil in a steam vaporizer helps. So does adding some coconut oil (organic, unrefined, cold-pressed, hexane-free) to her food:
Remedies for Kennel Cough - Whole Dog Journal Article
I've fostered dozens of dogs with KC. With antibiotics, they start feeling better in 48 hours, and are in good shape in a week.