Oops, I'm a Princess!

Luna's mother was accused of losing her virginity before marriage. She gave birth to Luna, who was called a bastard, and then killed herself. Luna was left an orphan with no one to claim her. The Prince Regent took her in and told her she was his daughter, and that nobody but him would be allowed to bully her. The emperor offered to make her a princess. The empress dowager was delighted to finally have a granddaughter, and the princes decided the small thing was their little sister. Luna can understand animals, and she uses it: she wins over the emperor's mother, saves a prince from poison, and gets in the way of a duke's scheming. Ordinary people around the capital start calling her the dynasty's good luck charm.