Her father dying heroically, in action.

Her grieving mother, sunk in consumption.
Becoming the foundling of her poor but honest Aunt and Grand mama.
Rescued from poverty by the fairy-godfather Colonel Campbell (who, like all fairy-godparents, bestows all the accoutrements of wealth and then vanishes without adding to her fortune by one brass razoo)
And now she returns, with all her elegance, accomplishments, and symptoms of delusive hopes, to become a governess.

It is not strange that Emma seeks some romantic intrigue to explain Jane Fairfax, but it seems extraordinary that a person with Emma's imagination could be so blind to this ready-made heroine (far more like a heroine than our own darling child).

Jane Fairfax's life story always seems to me, to be getting as close to the bounds of credulity, (although the germane details are perfectly plausible).
The only thing more astonishing, is Emma's prosaic attitude towards such a girl. Harriet's friend, the patron of orphans, sees nothing more exciting than the humiliation of having Jane Fairfax's diligent and persistent piano practice compared to her own.
If eleven swans flew down to greet Jane Fairfax when she arrived, I could see Emma dismissing the news with "Oh, yes, they come every year. She has been netting them some nettle-coats, I believe."