After court recessed, she gave a wan smile, stood up and put on a black coat before being led out of the courtroom by jailers.
Prosecutor Rick Unklesbay said the case was one "of overwhelming premeditated murder." He said Harrison planned the murder for days after Henderson accused her of stealing her student ID charge card, Social Security card, checks and $500 from a bank account.
Unklesbay said Harrison was a "master manipulator" who lied repeatedly to police after the murder. Harrison finally admitted to stabbing Henderson but insisted she had acted in self-defense.
Assistant public defender John O'Brien said Harrison was a naive, scared and confused girl who found herself unwanted as Henderson's roommate and worried she would be prosecuted because the theft accusations.
Outside court, Henderson's sobbing mother and father huddled with family members.
Nearby, Harrison's family also cried as they talked to their daughter's attorney.
Both families left court without speaking to reporters.
Harrison faces life in prison, and could be eligible for parole after 25 years depending on the results of a hearing before her Nov. 25 sentencing. Prosecutors had decided not to seek the death penalty.