For clarification, is your wife blind or otherwise a person with a disability? You mention that she had a service dog from a school that trains guide dogs for the blind. But you don't explicitly say she's blind herself. Because it's not clear from your post, I am left wondering whether she could be a seeing instructor/trainer for the school.

If she is not a person with a disability, then she is likely not protected by the ADA. It is incorrect for you to say that drivers must "transport anyone who has a support dog." The ADA prohibits discrimination against persons with disabilities, which would mean providing transportation to person with disabilities, which sometimes includes transporting service animals that perform tasks directly related to the person's disability. However, if the person with the dog is not disabled, then the person is not protected by the ADA, the dog is not considered a service animal, and a driver is not required to transport the animal.

Even if the dog is trained as a service animal (or is wearing a vest from the guide dog school for the blind), it is only a service animal when it is accompanied by a person with disabilities and performs tasks related to that person's disabilities. The ADA prevents discrimination against people, not animals. So it's not true that drivers must "transport anyone who has a support dog." It is only true that it is illegal to discriminate against a person with a disability, which might incidentally require transportation of a service animal for that person.

TL;DR: Bottom line, if she's not blind, then she's not protected by the ADA. If she's not protected by the ADA, then she has no legal recourse if a driver refuses service to her because she has a dog.