A judge has imposed a mandatory life sentence for an 18-year-old Pennsylvania woman convicted of instigating the torture killing of her one-time friend, who was mentally disabled.

Angela Marinucci of Greensburg was only 17 when 30-year-old Jennifer Daugherty was killed in February 2010 at an apartment about 30 miles east of Pittsburgh. Marinucci's age made her ineligible for the death penalty, which three of five other co-defendants will face at trials later this year.

Marinucci was convicted of first-degree murder in May. Prosecutors convinced a jury that Marinucci helped beat and humiliate Daugherty, who was forced to drink human waste mixed with drugs, because they were attracted to the same man, Ricky Smyrnes. The 25-year-old Smyrnes is among those facing the possible death penalty.

At her sentencing Wednesday, Marinucci apologized for not stopping the killing.