If she last played with other dogs on Sunday, then it *could* be kennel cough, which is highly contagious and takes 3 to 10 days to develop:
Kennel Cough: Signs and Symptoms
If it gets worse and it looks like she's having trouble breathing, I'd take her to the emergency vet to be on the safe side. But if it's just mild, occasional coughing, she should be okay until you see the vet tomorrow. Wishing the best for Chewie!