FAYETTEVILLE, N.C. — A Fayetteville teenager who admitted to shooting and killing her stepfather and testified against her mother in the case as part of a plea deal was sentenced Thursday to a maximum of 31 years in prison.

Last year, Elizabeth Shannon pleaded guilty in the 2002 slaying of U.S. Army Maj. David Shannon, but said her mother, Joan Shannon, convinced her to commit the crime.

In a deal with prosecutors, however, Shannon testified against her mother, who, on Aug. 31, was convicted of first-degree murder and sentenced to life in prison.

"I'm truly sorry," Shannon, who was 15 years old at the time of the crime, said in court Thursday. "I made devastating choices. I'll carry the shame the rest of my life."

Shannon told jurors that her mother first tried to poison Maj. Shannon and when that did not work, she gave the teen a gun and asked her to commit the crime so that she could be with a man she met at a party.

During Joan Shannon's trial, though, defense attorneys attacked Elizabeth Shannon's past, suggesting she was linked to gangs and that their client was the victim of a "lying daughter."

"I think her testifying was vital," said Assistant District Attorney Billy West. "We had to have the testimony of Elizabeth Shannon. I think we knew from the beginning."

Elizabeth Shannon's attorney plans to appeal the sentence, saying it is still too harsh. Meanwhile, Shannon and her mother will be housed in different prisons.