Why did Zhen Xuan kill the emperor?

The emperor spoiled her for three years, but her body always regarded her as the pure yuan queen. Her heart died, and she left the palace without leaving her three-day-old daughter.

Outside the palace, she fell in love with her brother-in-law They live a happy and beautiful life. He won't betray her. She is pregnant.

If she hadn't thought he was dead, she wouldn't have gone back to the place that made her miserable and disgusting. When she returned to the palace, she regained her favor and knew that he was safe and sound. But nothing can ever go back.

Later, their love affair was known to the emperor. The emperor asked her to kill him herself. She hates the emperor, and she is also afraid of the emperor, afraid that she, her children and her family will die at his hands. She is going to kill the emperor.