A northern Wisconsin woman changed her plea to guilty Friday in the slaying of her mother and stepfather in a deal that has prosecutors recommending a 40-year prison sentence.

Ashlee Martinson, who was 17 at the time of the March 2015 killings, faces two counts of second-degree homicide, USA Today Network-Wisconsin reported. She had earlier pleaded innocent by reason of insanity in the killings at the family's home near Three Lakes.

According to court records filed Friday, Martinson told police she shot her stepfather, 37-year-old Thomas Ayers, in the neck and head. She then went to her mother, 40-year-old Jennifer Ayers, for solace, but her mother first tried to aid her husband, then armed herself with a knife to confront Martinson.

Martinson wrestled the knife from her mother and stabbed her more than 30 times. She then went downstairs and turned the family TV to show cartoons to her three sisters, ages 2 to 9. After showering, Martinson confined the younger girls in a room before fleeing to Indiana with her boyfriend, documents show.

Court documents say the Ayerses were killed the same day they warned Martinson's 22-year-old boyfriend to stay away from her because she was a minor.

Martinson told authorities she had been mentally and verbally abused by her stepfather and had seen him physically abuse her mother and siblings, according to court records.

The assessment also said Martinson had suffered from depression on and off since age 8, gaining in intensity at age 15. Martinson's sentencing is set for June 17.