I think you are going to have to make your own mind up about this one.
Ideally you don't want your pup spending any time where there have been unvaccinated dogs - or foxes, of course. Betsy is not protected until a week after her second shot. Until then, she is very vulnerable. Parvovirus, for instance, can be picked up from the ground - and yes, foxes can have it too. I would not consider putting a young pup down in a public area such as the one you describe.