Before the Palace Intrigue Heroine Enters the Palace

[The male lead isn't chaste; the heroine is the most beautiful, but not kind]

A cannon-fodder character rises to become someone's moonlight (?):

Before entering the palace, Li Yushan accidentally glimpses the Book of Fate and discovers that the emperor she is supposed to marry is saving himself for his destined woman. She, meanwhile, is a cannon-fodder character with no name, appearing only in an extra chapter.

Fine, fine. In that case, she'll just give up and see what happens.

Unexpectedly, a mishap lets her claim the emperor's first night before anyone else, and she gets pregnant in one go.

But here's the question: in a story where both leads are supposed to be chaste, the male lead isn't. Will she, the woman who took his first time and bore his child, be promoted to heroine, or become the wicked supporting character the heroine gets rid of?

And with her in the middle, can the emperor and his destined woman still understand each other and spend their lives together?

Oblivious to it all, Li Yushan takes her child along to watch the drama unfold, not realizing that she has long since become part of the story.