She was found dead in her Fifth Avenue penthouse in 2007, the victim of a vicious beating that at first seemed a mystery but was later prosecuted as a case of an employee who exploited her boss' trust to steal thousands of dollars from her and killed to keep the theft quiet.
Lowery, who didn't testify at her trial, vowed to appeal.
"My innocence will continuously remain," Lowery said in a brief statement before she was sentenced. "This is just the beginning of a new fight, of a new beginning, to get a fair trial."
In words laced with tears and anger, one of Stein's two daughters reproached Lowery for not expressing regret for the crime.
"You are a disgusting person," Samantha Stein-Wells told Lowery in court.
"Where, where is your apology? Where is your remorse?"
Stein-Wells added as Lowery looked through documents at the defense table. "You are truly a cold, ruthless killer."
Lowery's lawyer and family said she had no cause to apologize for a crime she maintains she had nothing to do with.
"We are confident that, when all the issues are raised on appeal, Ms. Lowery will be cleared of these horrendous charges," said her lawyer, Paul Brenner.
Lowery helped the 62-year-old broker with clerical work and personal tasks, some of which Stein had trouble performing in the wake of breast cancer surgery.
Lowery, 28, admitted in a videotaped statement that she killed Stein but later recanted. In the confession, Lowery said she lashed out on Oct. 30, 2007, after the broker hassled her about the pace of her work and blew marijuana smoke in her face. No trace of the drug was found in Stein's body.
Lowery also was convicted of stealing more than $30,000 from Stein during their four-month working relationship.
In the hours after the killing, Lowery ran errands for Stein, went out to lunch with a co-worker, fielded phone calls for the broker and left messages for Stein and members of Stein's family - all efforts to cover her tracks, prosecutors said.
"Miss Lowery acted with an uncommon and almost inhuman degree of coolness and calculation, fully justifying the jury's conclusion that she took the life of Linda Stein intentionally," state Supreme Court Justice Richard Carruthers said at Lowery's sentencing.
Calling her "a very dangerous young woman," he said he would recommend she never be granted parole.
Lowery is the mother of a 2-year-old daughter, born while she was jailed awaiting her trial and now in the care of Lowery's mother and stepfather.
The case was been fraught with friction between the Lowery and Stein families, and between Lowery and her former lawyers.
Members of Lowery's family have repeatedly had outbursts in court; her stepfather now faces a criminal contempt charge after loudly denouncing Carruthers in March for refusing to let Lowery change lawyers. After one court date in 2007, Lowery's relatives accused Stein's daughter Mandy, who found her mother's body, of committing the crime.
"The tragic death of Ms. Stein is not something the Lowery family in any way condones," Brennan said Monday. He said "tragedy has also befallen the Lowery family" with her conviction.
Walsh and some of Lowery's other relatives quietly left the courtroom at points during her sentencing.
"I didn't want to hear it," Walsh said later, "because we know who Natavia Lowery is. She's a very good person."
In her appeal, Lowery will likely assail her prior attorneys' work and Carruthers' earlier refusals to let her drop them. She also opposed rulings that allowed jurors to see her repudiated confession and limited other potential evidence and witnesses, including an expert on the psychological reasons why some people falsely confess to crimes.
One of Lowery's former lawyers didn't immediately return a call Monday.