1. privileged
2. sexually innocent virgin -- educating a girl to never be alone with a boy, overprotective family (father, mother, brothers), and bodyguards requires money that few families have and time that few rich people are willing to spend on a daughter [the alternative being a convent school which introduces the danger that the girl may decide to become a nun instead of coming out as a debutante]
3. bright -- most gentiles breed out brains in both sons and daughters [which explains why the USA in general and The South in particular are sliding down world statistics]
4. encyclopedic knowledge of traditions (like old gazebos)

 

 

The purpose of such a daughter is to help Southern families gain or retain wealth and power.  It is not immediately obvious how a "silent influence" who stays out of public life can accomplish this but Southern belles become Southern ladies.  The atypical Southern belle will remain rare but will never disappear.