Margaret is a puzzle.
Meg works so well as a nn for the character, and then when her fashionable friends call her something else - was it
Daisy, like her future daughter? - it's just stylistically wondrous. And I've always wondered, if that sequence was based on reality, whatever
Anna could use as a nn instead of
Nan or
Nancy.
As for
Louisa, IRL she was
Louie =
Louis (m), so
Josephine, nn
Jo instead of
Joe, is a good stand-in.
Stephanie, for instance, would shorten naturally to
Steffie or
Steph, not
Steve, thus missing the point.