A tiny voice tells me we are overanalysing it, but... who cares, this is fun.

Emma: I think you are right that the first entence provides a good explanation- "handsome, clever, and rich". Nothing more to be desired for a woman in the era. Also, perhaps she is "complete" in the sense that she doesn't feel the need to be married?

Harriet: Maybe she became home ruler after she got married. Robert Martin made three miles road to fetch her walnuts (or whatever it was).