Youyou Si

She was the saintess of heavenly devil cult which was one of the three great sects, and the cult master's disciple, but her master fell in love with her and left his wife who he has been married for few hundred years to marry her. She killed her master on their wedding night and escaped with the demonic cult holy book which caused her to be chased down by her sect.

(Source: Tales of Herding Gods Wiki)