SOLVED. Story about an upper-class woman who falls in love with an undesirable man [s]

[Lobstergirl, au gratin]

Is it a short story, or a novel?

When did you read it?

Is it literary fiction or mass market fiction?

When and where is the setting? (Country, city, year, etc.)

[Kris]

Chad, why is the hero considered undesirable?

What else do you remember about her family? (e.g., location, background, interests)

[Samtran]

The novel you're thinking of is The Count of Monte Cristo...

What you are referencing is a part of a subplot to the main story; Valentine is the girl you are thinking of and she is a member of the Villefort family.

[Ayshe]

I second that it sounds very much like the The Count of Monte Cristo's subplot.
Except that there the father wanted the daughter to marry another, and the grandfather was disinheriting her should she do so.