Who is Princess Violet from Wizard's First Rule and what is their importance?

Although she is only a young girl, Princess Violet is already a sadist. She is plump and overfed, with thin wispy long hair, the sign of royalty. Princess Violet regularly slaps her companion Rachel, simply to see the look of surprise and hurt in the girl's eyes. She particularly enjoys taunting the defenseless orphan and making her sleep outside for imagined slights. Rachel has a doll when she first comes to live with Violet, but the Princess throws it in the fire in a fit of rage. She chops Rachel's hair in short spikes because the ugly Princess is jealous of Rachel's beauty.