A northern Wisconsin teenager accused of killing her mother and stepfather has pleaded guilty in a plea deal that has prosecutors recommending a 40-year prison sentence.

Eighteen-year-old Ashlee Martinson entered her plea on Friday to two counts of second-degree homicide. The teen had earlier pleaded innocent by reason of insanity.

Martinson was accused of fatally stabbing 40-year-old Jennifer Ayers and shooting 37-year-old Thomas Ayers at the family's home near Three Lakes in March 2015. Investigators said Martinson confined her three sisters in a room before fleeing to Indiana with her boyfriend. 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's a minor.

The sisters, ages 2 to 9, were not hurt.

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Information from: WSAW-TV, http://www.wsaw.com