@kneesox “femme fatale” is basically a word describing a strong cunning female villain. Femme fatale basically translates to “lethal woman”. They are very intelligent and fierce, and often use their charm and wit to get people to do what they want. They are always portrayed as evil, but no one in the story sees them for what they are until too late. The term originated from film-noir, which came into being in the 1940s. The reason why femme fatale are associated with men is because most film-noir protagonists are men, and most film-noir with femme fatale revolve around the protagonist being ruined by the femme fatale.
Wikipedia definition of femme fatale
So by definition, Becky of Vanity Fair crosses all the checklist of femme fatale, and she was around before film-noir was created.