Fifty-year-old Colleen LaRose had called herself "Jihad Jane" online and agreed in 2009 to kill artist Lars Vilks over his series of drawings depicting the prophet Muhammad as a dog. Vilks was never attacked.
LaRose faced a potential life term. But the judge accepted a government request to reduce the sentence because of her extensive cooperation with investigators.
Prosecutors still asked for decades in prison, saying she remains dangerous.
LaRose told the judge she became obsessed with jihad, saying she was "in a trance" and thought about it from morning to night.
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"I don't want to be into jihad no more," she said. Vilks told The Associated Press that he understands the principle of handing out tough sentences for terror crimes to deter others, but he said he felt the sentence against La Rose was too harsh.
"To lock her up for so many years seems like overkill to me," Vilks said. "This is a person who has been through a lot of difficulties in her life and needs mental care more than anything else."
LaRose could be out of prison in a little over four years, given the more than four years she has already served and the potential for time off for good behavior.
The Justice Department said Ali Charaf Damache, who was living in Ireland, recruited LaRose and another US woman via jihadist websites.
Damache married the other woman, Jamie Paulin-Ramirez, on the day she arrived in Ireland.