Li's identity in The Joy Luck Club is the younger sister of the Qing emperor (not related by blood). It stands to reason that she should get married when she comes of age. She will also have her own fief. After she gets married, she will either go to the fief or build a princess house in Beijing to live with the attached horse.
But Li doesn't want to get married. She wants to be with the Qing emperor.
The Qing emperor didn't force her because he knew Li's mind. Let her wander around Beijing for so many years, helping him with the affairs of the "library". In the first episode of the TV series, he declared his special trust in princess royal.
The Qing emperor's trust in Li was based on his firm belief that Li secretly loved himself and would never plot against himself. As for the lifelong happiness of princess royal, the Qing emperor never considered it. As for her fief, it is only reserved for her to collect rent.
Until Fan Xian grew up, he decided to take Fan Xian to Beijing to have a look and stir the pool of spring water in Beijing. In this way, Li can't sit still.
This story has been told for 46 episodes. Except Pingping Chen, Fan Jian, Qing Emperor and Wu Zhu, no one else knew that Fan Xian was the son of Qing Emperor. Lee obviously doesn't know.
Li doesn't want to lose her financial power in the cloud, because it will make her "useless." Over the years, she won the trust and favor of the Qing emperor by helping him manage the "Neiku". Fan Xian is too much of a threat to her. She must do something. So the Qing emperor got angry.
The Qing emperor was angry, not only because Fan Xian was his blood, but more importantly, he was the emperor. Who should be in charge of "Neiku"? Only he has the right to speak.
So, the Qing emperor said to Li: You crossed the line.
The Qing emperor drove Li to Xinyang, her fief. This Xinyang, I believe, is just a name invented by the author. Just like Teng Amethyst and Gundam, it has no special significance.