Note 1: (what all this elegance was destined to)
Jane Fairfax is destined to be a governess. Governesses were often in an awkward position. Depending on the family, they could be treated as mere servants or treated as nearly members of the family. Prior to arriving at a situation, it would be difficult for a young lady to know what will be expected of her by her new employer. Further, as an employee, and a woman forced to make her own way in the world and to earn her living, Miss Fairfax would lose much of her claim to be a member of the upper class. In addition, as a governess, she would very likely have to give up the possibility of ever being able to marry, have a home of her own, or ever having children.
The elegance that Miss Fairfax is destined to is, therefore, a decided lack of elegance.