U.S. District Judge Nicholas G. Garaufis also sentenced the former "Smallville" actress to pay a $20,000 fine and do 1,000 hours of community service. Her surrender date is Sept. 29, CBS2's Alice Gainer reported.
Prosecutors say she recruited women to a sex-slave subgroup of the organization.
Flanked by her mother and lawyer and surrounded by cameras, Mack left court with her head down and her hair covering her face. She did not answer questions outside, but in court the 38-year-old tearfully apologized, saying she was "filled with remorse and guilt," adding her actions were "abusive, abhorrent and illegal."
She said she was in a "cloud of delusion."
"Honestly, her eyes looked dead. It was very much that feeling of a sociopath," former NXIVM member Jessica Joan said.
The group, founded in Albany, New York by Raniere, was marketed as a self-help organization. But former members say Mack helped recruit women to a secret sub-society within NXIVM called "DOS" or "the vow."
The women had to give over collateral, like compromising photos and videos, in order to join.
Members were then organized in levels as masters and slaves.
Some women in DOS say they were branded with Raniere and Mack's initials, and other former members say they were also coerced into having sexual relations with Raniere.
In court, Joan referred to Mack as "the Ghislaine Maxwell to Keith's Jeffrey Epstein."
Joan said she doesn't accept Mack's apology and repeated what she said during her victim impact statement in court.
"She is a monster and a sociopath and she has created so much harm for me, her victims and so many people involved," Joan said.
During his remarks, the judge called Mack an "essential accomplice," and a woman who capitalized on her celebrity to recruit and manipulate women while hiding the true nature of the group. He also noted Raniere "could not have done that without you."
Though she faced up to 17 1/2 years behind bars, Mack's lawyers asked for no jail time. Federal prosecutors asked for leniency due to her cooperation.
"Now, we can really begin to heal. Justice has been served," Joan said.
Mack has been on home confinement at her parents' house in California. She said she has reunited with her family and is rehabbing herself, taking online college courses.
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