The twins' mother Boo Jun Kim, breaks down in Orange County Superior Court during the trial
Judge Eileen Moore, passing sentence in the Central Superior Court, in Santa Ana miles rejected attorneys' arguments for a new trial and for leniency for Jeen "Gina" Han.
"It is obvious Miss Han is a danger to society, particularly against her family," the judge said.
Prosecutors said that in 1996 she had sent two teenage boys, who were convicted with her, to her sister's flat.
The murder plot was foiled when police arrived on the scene.
Jeen Han said she never intended to kill her sister.
"I'm deeply sorry for everything that has happened," Jeen Han said. "I just feel very bad and extremely remorseful for all the pain I have caused to my sister, my community and to my entire family."
Jeen Han's sister Sunny was not in court to hear the sentence.
A few years ago, the twins shared the limelight as high achievers at their school.
During the trial last year, authorities at first suggested that Jeen Han had wanted to kill her sister and assume her identity in a case of "good twin-evil twin."
But during a preliminary hearing, a picture of sibling rivalry emerged, in which Sunny was said to have once apparently tried to have Jeen arrested for stealing her car.
Sunny - who at one point during the trial collapsed on the witness stand after taking an overdose of sleeping pills - also said at that hearing that she did not believe her sister wanted to kill her.