Viviana Gunn, 34, pleaded guilty in a deal with Kitsap County prosecutors.
The Kitsap Sun reports her husband, 27-year-old Brandon P. Gunn, also pleaded guilty and faces a sentence of more than 30 years when he is sentenced Jan. 17 in Port Orchard.
The teen is the man's brother who came to live in the couple's Silverdale home in May 2013.
He told sheriff's deputies the couple beat him with a baseball bat, sliced his skin with a heated knife, forced him to remain naked in a portable dog kennel without food and water and once drove a nail through his palm.
The alleged abuse began soon after the boy's arrival when he told police he was punished for shoplifting.
The teen recounted horrifying "assault sessions" which he says occurred in the residence's garage, cellar, and bedroom. In one account, the teen told police the couple beat him unconscious with either a baseball bat or metal bar. He says he was bound to a chair, and sometimes hung from a rafter when these beatings occurred.
Recounting a particularly gruesome memory, the 13-year-old told police that his abusers "placed his hand in a bench vise, tightened the vise jaws and drove a nail through his hand with a hammer."
He says the hammer was also used to hit his feet repeatedly, he was forced to strip, and was imprisoned inside a portable dog kennel for days without food or water. The kennel was secured with a ratchet device to prevent escape, according to police reports.
Police say the teen told them his older brother stapled his hands with a staple gun, and his sister-in-law cut him with a heated knife.
The teen told investigators the sessions which included beatings, burnings, and other forms of torture began earlier this summer, and continued for weeks until he managed a daring escape.
During the last session, the teen says his hands, feet, and mouth were taped shut as he was beaten with a baseball bat. The teen claims he was able to chew through the tape and finally escape.
The teen was on the run for 2 weeks. He was living in an abandoned house, and shoplifted to eat, according to police. He never asked for help, and police say his guardians never reported him missing.
On Facebook the boy's aunt who lives in Georgia lashed out at the couple. When she didn't hear from the 13-year-old, she reported him missing.
Weeks later, Bremerton Police found the teen badly wounded on a park bench. Investigators following up on the teen at the hospital alerted authorities of the alleged abuse.
Detectives searched the Gunn's residence and say they found evidence substantiating the teen's allegations.
The boy's mother told authorities she moved her teen son from Georgia to live with his brother in Silverdale so he could have a male role model.
He has now returned to Atlanta to live with his mother.