Ruth Christine, originally from Launceston in Cornwall, was sentenced to 90 months at the hearing in Roseburg, Oregon.
She and her American husband went on the run in August 2001 with their three daughters, who had been taken into care after fears of mistreatment.
Her husband Brian Christine was jailed for 12 years for pointing the gun used in the kidnap.
Foster care
The family was living on a bus when police in Grants Pass, Oregon, took Bethany, six, Lydia, four, and Miriam, three into care.
Doctors said the children were malnourished, and they spent several days in hospital before being place in foster care.
But during a supervised visit to the children in August 2001, Mr Christine put a gun to a social worker's head.
The couple fled with the girls, but were arrested several days later in Montana after being stopped for speeding.
The Christines, who met at the University of Kent in the mid-1990s, were convicted in May of robbery, custodial interference and unauthorised use of a vehicle.
Ruth Christine, 29, told the court she was sorry for the trauma suffered by the two welfare workers.
"Today, all I want is to be with my husband and children," she said.
Further charges
The couple's unorthodox lifestyle won them support from campaigners, who held rallies outside the courthouse.
Mrs Christine also appeared on several TV debates.
The girls have now been adopted by her parents and are living in Cornwall.
The Christines face a separate trial on criminal mistreatment charges in July.
Paul Tyler, the MP for North Cornwall, said it had been a "traumatic" time for the family.
He said his own children had known Ruth quite well.
"They would all be amazed, horrified and dismayed by the extent to which she seems to have been under the influence of her husband during this whole horrible, tragic episode."