Cain and Diana's parents also want to maintain that commoners are commoners and nobles are nobles, forever separated, mentality, so Cain indeed needs to work hard to make sure Diana won't develop the kind of personality that believes a noble must never be worse than a commoner at anything at all. After everything he has done so far, though, Diana is not the same person anymore she used to be in the game. It might be good to have her interact more with commoners (outside of their palace), though, so that she will develop an inherent respect for their input into the society and lives, even if he still made sure not to cross the line their father has set, at least not too much. A number of years still remain until the game plot period, so Diana could still change in the worse direction, should Cain leave Diana at the mercy of their father.