If you think about it there are sick
dogs in and out of your vet all the time. You bring your dog
in and they can easily pick something up. May sound crazy but I always wipe my dogs paws down when we get back from our vet or dog park just to be safe.
Try not to worry too much, you can make yourself crazy trying to think about the causes of how your dog got sick. You are taking care of it now and thats what counts.
If she is not better, I would bring her back to your vet.