Ms. 45

While walking home from work, Thana, a mute seamstress in New York City's Garment District, is raped at gunpoint in an alley by a mysterious, masked attacker. She survives and makes her way back to her apartment, where she encounters a burglar and is raped a second time. Thana, her name an allusion to Greek god of death Thanatos,[2] hits this second assailant with a small sculpture then bludgeons him to death with an iron, and carries his body to the bathtub. She goes to work the next day, and after encountering working with an iron, watching her boss Albert rip a shirt off a mannequin, she goes into shock state, which worries her co-workers. However, when she looks at the trashbin at her office, she decides to dismember the burglar's corpse and throw the parts away in various locations of the city.
After being sent home, she dismembers the burglar's body, then keeps his .45 caliber pistol, puts the pieces into plastic garbage bags, and then stores them in her fridge. After cleaning her bathtub, she decides to take a shower, but as she strips, she begins to hallucinate the first attacker in the mirror grabbing her breast. This puts her into shock, and notices that organs and body fluids from the burglar are overflowing in the drain. Her neighbor, an old, recently widowed woman named Mrs. Nasone who owns a small dog named Phil, also starts to notice her odd behavior.
On her walk home from work the next day, Thana is noticed by a young man on the street while she is disposing of one of the bagged body parts; thinking that she accidentally dropped the bag, he retrieves it, frightening her. He chases her through the alleys of the city, and fearing another sexual assault, she fatally shoots him when she is cornered by him. The event furthers her impulse for vengeance. While running home from the incident, Mrs. Nasone notices she ran up the stairs violently and started throwing up. She insists in calling a doctor for Thana, and Mrs. Nasone's dog, Phil, starts to become attracted to her fridge. Thana escorts her out of her apartment while still in shock.
As the limbs start to bring attention towards the media, Albert brings her into his office and notices she hasn't been selling and feeling well lately. He decides to invite her to a Halloween party that he is throwing for work, and tells her that there will be "many boys there [her] age". She responds to him in writing, saying "I'll try". As Thana's vengeance increases, she starts regularly targeting and killing multiple men, such as a bisexual fashion photographer, a pimp who assaults a prostitute because of debt, multiple members of a gang, a Saudi Arabian businessman and his limousine driver, and even drives a recently dumped salesman to suicide after her gun jams.
Albert begins to notice that she ditched work after going to dinner with her co-workers, resulting in her co-workers having to finish her work. However, she promises to go to the party with him in exchange for staying out of trouble for her absence. Thana later appears to kill Mrs. Nasone's dog, after she notices that the dog is attracted to the smell of the burglar's limbs. She leaves a note saying that Phil ran away and will probably find his way back home soon. At the party, she dresses up as a nun with red lipstick and attends with Albert as a couple. Meanwhile, Mrs. Nasone goes into her apartment and finds the burglar's dismembered head, and determines that she killed Phil, and tells police that is at a party with her co-workers. While going upstairs in private, Albert tries to seduce her, and in revenge for his borderline-sexual behavior towards her in the past, she shoots him. The party stops and her co-workers run upstairs towards Thana, but then soon realize that she was the murderer when she steps out of the room with her pistol. Thana then begins a shooting spree and targets many of the men present. Her co-worker Laurie notices the knife that was used to cut the cake, and without Thana noticing, is stabbed by her behind her back, but not before turning around to acknowledge who it is. Thana appears to scream in pain "sister", falls to the ground and dies.
After the party massacre, Mrs. Nasone is seen crying, in memorial for her husband, Thana, and Phil. Outside her apartment door, Phil is shown running up the stairs and waiting by the door for Mrs. Nasone to let him in, indicating that Thana didn't kill Phil like presumed.

Question: Why She targeted and killed multiple men?
Answer: As Thana's vengeance increases, she starts killing multiple men.