An Idaho woman blamed mental illness and substance abuse as she pleaded guilty to scalping a teenage girl, saying she only intended to give her a haircut.

Marianne Dahle (search), 26, of Caldwell, pleaded guilty to aggravated battery before 4th District Judge Kathryn Sticklen on Wednesday, the day her trial was to begin. Sentencing has not yet been set, and Dahle could face up to 15 years in prison.

Prosecutors said Dahle tied up a 15-year-old Nampa girl — who has been identified publicly only by the first name of Sheila — on Jan. 18 and used a 4-inch knife to cut away the entire crown and back portion of her scalp. The attack happened at Kirkham Hot Springs, 70 miles northeast of Boise (search), where Dahle had invited Sheila and a 16-year-old female acquaintance to soak in the pools of warm water and party.

Investigators said they believe Dahle and Sheila were part of a clique of young female "punkers" who wore mohawk haircuts. Police say according to the group's creed, if a member disrespected women, they were not allowed to wear a mohawk. They believe Dahle scalped Sheila in retaliation for actions the younger girl had made that Dahle perceived as offensive to their gender.

In court Wednesday, Dahle acknowledged she scalped the girl, but said she only meant to trim her mohawk.

"The things that you said happened, but it was not intentional," Dahle told Sticklen, according to the Idaho Statesman newspaper.

Dahle's attorney, Kathy Edwards, said the woman planned to shave the girl's mohawk but forgot to bring a razor with her to the hot springs and used a knife instead. She added that Dahle has a history of mental illness and was not taking her prescribed medications at the time of the scalping.

"(Dahle) understands that she bears responsibility," Edwards said. "She wants to acknowledge what she did ... and spare the victim from going through a trial."

Neither Sheila nor her mother attended Wednesday's hearing. The girl spent two weeks in the hospital while doctors used skin from her thigh to cover the six-inch-by-eight-inch circular patch of missing skin on her crown.

After the attack, Dahle allegedly drove the blood-covered victim to a Boise hospital and left her, then disappeared for several days before turning herself in.

The 16-year-old girl who was with Dahle and Sheila at the hot springs has not been charged in the case because investigators said she was a cooperative witness and they determined Dahle was solely responsible for the attack.