Scout compares Alexandra to Mount Everest: "She was cold and there." Scout finds Alexandra to be "cold" because she rarely expresses any feeling or emotion except perhaps disapproval, which is almost always directed at Scout's clothing, or behavior, or some combination of the two. Scout finds Alexandra to be "there" because she is Atticus's sister, thus a part of the family, and an inevitable part of Scout's life.
Scout also had a unique assessment of Alexandra's general appearance, commenting that the clothes Alexandra chose "managed to suggest that Aunt Alexandra's was once an hour-glass figure. From any angle, it was formidable."