Mansfield connects New Zealand to the woman at the store with the following quote:
There is no twilight in our New Zealand days, but a curious half-hour when everything appears grotesque—it frightens—as though the savage spirit of the country walked abroad and sneered at what it saw. Sitting alone in the hideous room I grew afraid.
The "hideous" room is the woman's parlor. Like New Zealand at a certain time of day before darkness falls, the woman at the store is "grotesque": she is missing her front teeth, is angry, resentful, and unfriendly, and complains of being lonely, saying her husband has left her once again to go do the sheep shearing.
The sense of fear and foreboding that the darkening New Zealand landscape brings is like the sense of fear and foreboding the narrator feels about the woman. She, too, seems to her like the "savage spirit" of the countryside. Sitting in her room, the narrator appears to become fearful of both the countryside and the woman.
Jim insists that when he met the woman four years ago, she was a beautiful barmaid. The harsh New Zealand countryside seems to have left its savage mark on her. She complains she has had four miscarriages and implies they were caused by her husband's abuse.
The narrator's fears about the woman will be realized after her daughter shows her a drawing she had done that suggests that her father is missing because her mother shot and killed him. Like the harsh, "grotesque" landscape, the woman has become harsh and "grotesque."