especially when he can see her in the backyard).
Presuming that the yard is enclosed/fenced, why not have him outside with her?
Because you are presuming incorrectly! That said, he has gotten much less anxious as he is more used to the house and people going in/out.
Neighbors did finally put a fence up in back though (new houses got built very close to ours).. now I'm looking for something to block off the part of the yard that is exposed between the garage and house. Hard to find something that stands out or, mainly, taller than 3 feet