The idea of a femme fatal is an archetype found uniformly in ancient cultures. It is also an archetype in the Jungian collectively inherited unconsciousness. The traits of the essential femme fatal (there are some variations) are as follows.
The femme fatal is primarily an aggressive seductress. Her aim is to create compromising circumstances, think Delilah to Samson. The femme fatal is powerful. She has a flavor of the exotic about her. She can wrap powerful men around her little finger, as the saying goes. She is known for her seductive powers, her allure and her charm. She torments her prey by not returning their enrapt affections. On a variation of the femme fatale, she may repent and change her ways.
In The She-Wolf, Nanni's mother-in-law is a femme fatale who exerts her beguiling and destructive power over him to a degree of creating obsession and irrational, moral exhaustion. She drives him to the point of extraordinary action to escape her bewitching, dark spell.