What does Aunt Alexandra contribute to the Finch family in To Kill a Mockingbird?

Scout's Aunt Alexandra is the sister of Atticus and wife
of Jimmy Hancock; Alexandra and Jimmy live at the old homestead at Finch's Landing, 25
miles west of Maycomb. Alexandra and Jimmy aren't the happiest of couples, and they seem
to prefer as much distance apart as possible. Alexandra's own parenting skills are
questionable, having produced a son, Henry, "who left home as soon as was humanly
possible;" her grandson, Francis, "was the most boring child I ever met," according to
Scout. Nevertheless, Alexandra decided that Atticus' children needed a motherly touch,
and she invited herself to come and stay with Atticus in Maycomb at the onset of the Tom
Robinson trial.

After losing her battle with Atticus to rid
the household of Calpurnia, Alexandra settled down

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... and life resumed its daily pace. Aunt
Alexandra seemed as if she had always lived with us... she had river-boat,
boarding-school manners... she was an incurable gossip... She was never bored, and given
the slightest chance, she would exercise her royal prerogative: she would arrange,
caution, advise and
warn.

Alexandra believed that
Atticus' home needed a feminine touch, and that both children were in want of a mother
figure. She believed that Scout specifically was in need of ladylike qualities, and
Alexandra did her best to see that Scout was converted from tomboy to little lady.
Alexandra refused to allow Scout to invite Walter Cunningham Jr. to visit, telling Scout
that "he--is--trash!" and not worthy of socializing with a Finch. She worried about the
repercussions of Atticus defending Tom, and she feared that the family might be in
danger after the threats made by Bob Ewell.

But by the end
of the novel, Alexandra seems to have found some acceptance from Scout and Jem. Scout
admires her ladylike skills at the missionary tea, and Alexandra blames herself for
Bob's attack on the children, since she decided not to escort them to the Halloween
pageant. In the final chapters, she lovingly tends to Jem's injuries, and in a rare
example of giving in to Scout's tomboyish tendencies,
she

...
brought me my overalls. "Put these on, darling," she said, handing me the garments she
most despised.