What were Zenia's most significant actions and what were the effects of those actions?

Zenia takes a number of actions that the other characters see as significant betrayals. It's best to review her relationship with each of the other female characters and discuss what she does to betray each woman.
Charis is a very sensitive character who tries to help Zenia when she claims to be very ill. Charis allows Zenia to live in her home with her and her boyfriend Billy. Although the women already seem to know that Zenia is not trustworthy and that she possibly lies about her background, Charis takes pity on her. Eventually, Zenia begins an affair with Billy and they run off together. They even violently kill Charis's chickens and leave the mess behind for Charis to find.
Roz is a working woman who seems strong and has a vivacious personality. However, she also falls victim to Zenia's betrayal. Zenia seduces Roz's husband, eventually driving him to commit suicide. Roz also helps Zenia by giving her work at the magazine Roz runs, and Zenia ends up surpassing Roz in some ways, which feels like another betrayal to Roz.
Tony is an intellectual, a professor who studies war and battles. Tony's eventual husband, West, was once in a relationship with Zenia, who treated him poorly. Tony and Zenia meet as students, and Tony writes a paper for Zenia. She uses that against Tony later on, and at one point, when Zenia returns to Tony's life, she rekindles a relationship with West until Zenia discards him yet again and returns to Tony.
Zenia is depicted as a woman who preys on the weaknesses of other women, but she is also someone who seems to enjoy luring men away from those women. We never hear Zenia's perspective in the story, so we cannot know her motivations; she remains a mystery to the reader as well as to the characters, who can only develop an idea of her from the treacherous acts she performs against them.