Marlene felt very embarrassed at Li FuJin since it was her who gave him a one sided condition; to make a Nuòyán and do whatever she wants in return for her help to change his identity.
Truthfully, being a witch who will make a Nuòyán with a higher being only means being a slave. But does she worry about it? No! Marlene didn't give a sh*t about those things!
Marlene made up her mind to completely throw her reputation as a witch queen. She has her own reason why she chose to be a contracted witch.
Since Li FuJin has a higher blood. A mixed on his veins, Marlene decided to become his contracted witch; to be with someone strong enough who she can ask for help to protect her son.
Why? That's because Xi'an is a mixed blood. Marlene runs away from Xiao XiRan so he won't be in danger, to prevent receiving the punishment of annihilation due to a repeated mixed blood.