Alyssa Barrett pleaded guilty to murder charges in December, saying she was there when her mother, Decarol Deloney-Cain, was killed in July 2014.
The body of the 54-year-old United Airlines flight attendent was found int he trunk of her car in a wooded area of Gary, Ind.
A total of four people are charged in relation to Deloney-Cain's murder. Barrett and her boyfriend Damarius Wren were both charged with first-degree murder, while a 17-year-old boy and 18-year-old boy were charged with assisting a criminal.
According to an affidavit, Wren admitted to police that he killed Deloney-Cain in her home, put her body in the trunk of her car and left the vehicle in Gary. She had been stabbed, beaten, bound and her head put in a pillowcase before her body was wrapped in plastic, police said.
Alyssa was 17 at the time of the murder and says she lied to police to cover up the crime. A plea agreement calls for her to be sentenced to 50 years in prison.