The younger sister is really narrowminded, naive, stubborn and spoiled by the people surrounding her and their parents, useless to correct her, leaving the elder sister to scold and correct her behaviour = evil in the eyes of the people who like her careless behaviour and don't know it better themself.
She is practically in a way of self-destruction in the futurefor that time, unless she has competent people arround her, I mean she could start a rebellion against royality and nobility with her stupidity, along with the 'kind and righteous behaviour' to commoners and don't forget she is one of these priviledged people herself... hopefully we won't see much more of that pest of a younger sibling after going to the north.