Sharing a Body with the Wicked Immortal Emperor

Looking for a Novel About Two Souls in Another World, Transmigrating to Ancient Times, Which Turns Out to Be a Cultivation Story

I think the female lead is called Xiaoxin. When she first transmigrates, she's a snake. At that point, the male lead is a monk, but he's actually the crown prince of a kingdom. Please, if anyone knows the title, tell me!