She was originally the prince's fiancée, but the prince fell in love with her sister.
When they got hairpins, they exchanged marriages. The sister-in-law who was supposed to be Princess Yun became the Crown Princess, and she, the Crown Princess who the matchmaker said she was, became Princess Yun.
She is not a kind little white rabbit.
Um! Prince Yun is pretty good-looking, so I'll accept it!