She is a rich girl. Apparently everybody who goes to Tokiwadai is rich. It's obvious she was born an ojou-sama since nobody who had to make riches through hard work wouldn't behave so. However, I believe that's the whole point and charm of such characters.

All the more reason for Mikoto and Touma to become a pair: One is too rich to realise the worth of money and one is so poor that getting food can become a problem. They would balance each other nicely.