Google holistic vet care and read for about a minute. Call them back and tell them that you have researched the topic and can see their point. Get the dog and do as you see fit. Same nuts probably don't vaccinate their kids.
I tend to agree here. I'm on my third GSP and have a 4th arriving on Memorial Day. These dogs are happiest in the fields, in the woods or in the lakes. With Lyme's disease and canine flu all over the place, you would have to be batshit crazy not to vaccinate your dogs.
Mind sharing the rescue that has her? I would like to vet through my GSP group and get their feedback.
