Cat People

Irena Gallier travels to New Orleans from Canada to reconnect with her brother Paul. Both orphaned after their parents died, Irena has been in foster care her entire life. Paul, not so lucky, spent his childhood in and out of institutions and jail. They return to Paul's home where his Creole housekeeper Female (pronounced feh-MAH-leh) helps Irena settle into her brother's house. Later, as Irena sleeps, Paul watches her with a predatory stare. That same night, a prostitute walks into a fleabag motel to meet a johnÂ â and is instead mauled by a black panther. The police capture the panther, aided by a team of zoologists: Oliver Yates, Alice Perrin, and Joe Creigh.
That same morning, Irena wakes to find her brother missing. Female guesses he went to the mission, and will be home later. She pushes Irena to enjoy New Orleans on her own. When Irena visits the local zoo, she is drawn to the newly captured panther, and stays long after closing hours. When Oliver, the zoo's curator, discovers her, she runs and scales up a tree. Oliver calms her, takes her to dinner, and eventually offers her a job in the gift shop. Irena enjoys her time working alongside Oliver and Alice, until one day she witnesses the new panther rip Joe's arm off during a routine cage cleaning, which leads to Joe's death. Oliver resolves to euthanize the cat, only to find that the animal has escaped, leaving behind a puddle of melted flesh and viscera in its cage.
Soon, Paul turns up and tells Irena of their family's werecat heritage. If a werecat mates with a human, the werecat transforms into a panther, and only by killing a human can the werecat regain human form. He also tells her that their parents were actually brother and sister because werecats are ancestrally incestuous and only sex with another werecat prevents the transformation. He makes a sexual advance towards his sister in the hopes that she will understand their predicament and accept, but she doesn't, and flees. She runs and flags down a police car, only to have second thoughts about turning her brother in. But it is too late, a police dog catches the scent of something within the house and a detective is called in. In the Gallier's basement, police find shackles, bones, and remains of dozens of corpses. They figure a wild animal was housed in the basement and call in Oliver to have a look.
On the run from her dangerous brother, Irena takes refuge in a frustrated romance with Oliver, afraid of what might happen if she has sex with him. One night Paul (in panther form) breaks into Oliver's house, intent on killing him so he can have Irena to himself, but is shot by Alice. Oliver performs an autopsy on the panther, cutting it open, a green gas escapes and he discovers a human body within the cat. Before he can document the finding, the animal has melted into the same flesh and viscera pool as before.
Irena is now trapped. Paul was the only person that it was safe for her to mate with. If she takes a human lover, she will have to kill to regain human form. Eventually, Irena has sex with Oliver, transforms into a panther and flees, sparing Oliver's life. She escapes, but is later trapped on a bridge by police. Shortly after Oliver arrives at the scene, Irena sees him and jumps off the bridge and escapes. Oliver realizes where she is headed and confronts Irena at a secluded lake house, she having regained human form by killing the house's caretaker. Irena tells Oliver she did not kill him because she loves him, and begs him to let her "be with her own." Oliver ties Irena's arms and legs to the posts of the bed and proceeds to have sex with her, knowing what she will become.
Later, Oliver is at the zoo working. By this time, he and Alice are romantically involved. He walks to a cage that contains a black panther, implied to be Irena, casually hand-feeding and stroking the animal.

Question: Why did Irena not kill Oliver?
Answer: She loves him