The Girl with the Dragon Tattoo

In December 2002, Mikael Blomkvist, publisher of Millennium magazine, loses a libel case involving allegations he published about billionaire financier Hans-Erik WennerstrÃ¶m. He is sentenced to three months in prison and a hefty fine. Lisbeth Salander, a brilliant but damaged surveillance agent and hacker, is hired by Henrik Vanger, the patriarch of the wealthy Vanger family, to investigate Blomkvist. Vanger then hires Blomkvist to investigate the disappearance of his niece, Harriet, who vanished on Children's Day in 1966. Vanger believes that Harriet was murdered by a family member.
Salander, who was ruled mentally incompetent as a child, is appointed a new legal guardian, Nils Bjurman, after her previous guardian suffers a stroke. Bjurman, a sexual sadist, forces Salander to perform fellatio on him in return for the money she needs to buy a new computer; he withholds the full amount she has requested. At her next meeting with Bjurman, he beats and rapes her. Having used a hidden camera to record Bjurman raping her, Salander returns to take her revenge, torturing and threatening to ruin him unless he gives her full control of her life and finances. She then uses a tattoo gun to brand Bjurman's abdomen with the message "I am a sadist pig and a rapist".
Blomkvist moves to a cottage on the Vanger estate and meets the Vanger family, including Harriet's brother Martin and cousin Cecilia. Inside Harriet's diary, he finds a list of five names alongside what might appear to be phone numbers. He visits retired police inspector Morell, who informs him that his investigation team had been unable to decipher them. After viewing photographs taken during the Children's Day parade, Blomkvist sees Harriet's facial expression change suddenly just before she leaves and, after obtaining photographs taken from the same side of the street as her, comes to believe that Harriet may have seen her murderer that day.
Using her access to Blomkvist's computer, Salander learns that the numbers in Harriet's diary are references to verses in the Book of Leviticus and emails Blomkvist anonymously. Blomkvist works out that Salander sent the mail and hires her as a research assistant. Together, Blomkvist and Salander connect all but one of the names on Harriet's list to murdered women. They are all Jewish names, which intrigues Blomkvist, as the Vanger family has a long history of antisemitism. During the investigation, Blomkvist and Salander become lovers.
They suspect Henrik's reclusive brother Harald to be the murderer, as the two other Vanger brothers had already died by the time Harriet disappeared. Salander searches through Vanger's business records to trace Harald to the crime scenes, while Blomkvist breaks into Harald's house, believing it to be unoccupied. When Harald attacks Blomkvist, Martin appears and saves him. He escorts Blomkvist to his home, where Blomkvist reveals what he and Salander have uncovered. Martin drugs him. Salander's search of the company accounts points to Martin and his late father, Gottfried, having been jointly responsible for the murders. She returns to the cottage to find Blomkvist missing.
Blomkvist wakes to find himself bound in Martin's cellar. Martin boasts about raping and murdering women for decades but denies killing Harriet, insisting that she disappeared. As Martin is in the process of hanging Blomkvist, Salander appears and attacks Martin with a golf club. While she frees Blomkvist, Martin flees in his car. Salander gives chase on her motorcycle. When Martin drives off the road, Salander finds him still alive but trapped in the vehicle. As the car goes up in flames, she makes no attempt to save him.
Blomkvist realizes that Cecilia's late sister Anita was the near-double of Harriet and that some of the film taken on the day of Harriet's disappearance show Anita, not Harriet as previously thought. Blomkvist and Salander discover that Harriet has been using Anita's name and is still alive in Australia. Blomkvist flies there to look for her, and he persuades her to return to Sweden, where she is reunited with her uncle. Harriet explains the truth about her disappearance: that her father and her brother had repeatedly raped her; that she killed her father by drowning him, only to find herself being blackmailed by Martin; and that her cousin Anita had smuggled her away from the island.
Salander's mother, living in a nursing home, apologizes for not choosing a "better papa" for her. Salander then visits Blomkvist in prison and gives him new information on the WennerstrÃ¶m case. After his release, Blomkvist publishes a new story on WennerstrÃ¶m in Millennium, which ruins WennerstrÃ¶m and makes the magazine a national sensation. WennerstrÃ¶m is then found dead, a presumed suicide. His offshore bank account in the Cayman Islands is raided; the police suspect a young woman caught on CCTV, whom Blomkvist recognizes as Salander in disguise. The film ends with Salander, dressed very smartly as she exits her car, walking along a sunny beach promenade.

Question: Who is Cecilia's late sister?
Answer: Anita