I was wondering how other sitters handle unvaccinated dogs. I require all of my guest dogs to be current with their vaccines and I will not take them if they are not. They also have to give me a copy of their vaccination records. How would you handle a customer who does not believe in vaccinating their dog? She believes it's not necessary. I have not come across this yet but I know of someone who refuses to vaccinate their dogs.
I haven't come across any unvaccinated dogs yet and, like you, do require all dogs to be current. If I were approached about taking one in, I am afraid I would just turn it down, just as a kennel would. People who make those decisions about their dogs need to deal with the ramifications themselves.
If she wants to use Rover, I would suggest looking for a sitter who does not have a dog and only accepts one dog or hire a traveling sitter to tend to her dog in her own home.
It's a personal judgement call for the sitter. I always ask ... as my dog is always kept current too, so it's important to me. I've found that most often the dogs are not vaccinated due to age (either puppy or senior, especially if ailing health - in which case sometime it's the vet recommendation to not). I also mention it in my profile.