I have often thought this as well. Not only regional accents but regional phrases, figures of speech or grammar could help narrow down where she could have grown up. When I think of someone with no accent I actually think of the lower midwest (Iowa, Illinois, Ohio, etc) more than I think of the Western states. To my ear, people from California/Washington/Oregon have a specific regional dialect, though it is less obvious of an accent than Southern or New England accents there IS an accent to the west coast, IMO. I haven't known enough people from Arizona or Idaho to judge what their accent is like but I bet there are tells that natives of those states would detect as well.