How might the reader's impression of Aunt Alexandra be different if Lee had written the story in third person?To Kill a Mockingbird by Harper Lee...

If Harper Lee had written in third person, we would see
more of a description of Aunt Alexandra's position and social standing and how it
relates to her demeanor toward the Finch children.

During
the time that this story was written, women primarily gained social standing through the
career and position of their husbands in the community, through church or social work,
or through entertaining at their homes.

Aunt Alexandra
strongly feels that Atticus is not teaching his daughter the necessary skills required
to be a successful woman in the culture i.e. a true Southern Belle. It is obvious that
Alexandra cares deeply for the children because she confronts her brother regarding
their lack of "appropriate dress"  and manners since Scout prefers overalls to dresses.
She makes herself available to the family during the trial of Tom Robinson as a
caregiver to the children. She upholds her brother's representation of Tom Robinson to
her friends at the tea party. In Scout's eyes, this character blossoms for the reader as
the climax of the novel is reached and the news of Tom Robinson's death is revealed at
the tea party.

We only see Aunt Alexandra through the eyes
of Jean Louise Finch (Scout) and are left to form a rather biased opinion of this woman
based on the very limited exposure we are given to her character. It is Alexandra's
stiff upper lip that Jean Louise adopts in the face of the terrible
news.