McGrath died Friday at Community Memorial Hospital in Ventura of an infection resulting from a chronic illness, said her daughter, Laura D'Auri. McGrath was taken to the hospital on Thanksgiving.
McGrath's role in the infamous trial was celebrated in Luis Valdez's play "Zoot Suit," which debuted at the Mark Taper Forum in 1978 and was made into a movie in 1981.
"She was one of the heroines of the 20th century," said Valdez, who remained a friend over the years. "In Los Angeles, I can't think of many people who surpass her influence."
McGrath was 24 when, recovering at home from a bout of pleurisy, she was visited by a friend who asked for some administrative help. Attorney George Shibley was defending 22 Mexican Americans, ages 17 to 21, who were charged with killing a young Mexican farmworker near a swimming hole in southeast L.A. County known as Sleepy Lagoon.
Shibley needed someone to write summaries of the daily proceedings of the trial, which would later become known as one of the most racist in local history.
The defendants, dubbed "zoot suit gangsters" by a xenophobic press after the long coats and pegged pants that were popular among Mexican Americans, were being tried en masse. Portrayed as members of the "38th Street Gang," they were not allowed to consult with their lawyers during the 13-week trial. And in a tactic that made them look disreputable, they were not permitted to have their hair cut and were denied a change of clothes for the first month of the trial.
The judge was openly contemptuous of the defendants and their lawyers, and the all-white jury was allowed to go home at night, with access to sensationalist media coverage that focused on Mexican American delinquency.
Twelve were convicted of murder and the rest of lesser charges.
McGrath, who attended the trial after her illness subsided, was outraged, and began to volunteer with the Sleepy Lagoon Defense Committee, which lobbied for an appeal. Committee head and renowned author Carey McWilliams was impressed with her passion and named her executive director.
McGrath would become an accomplished fundraiser and speaker, at one time addressing 1,000 longshoremen in San Francisco. She regularly visited the Sleepy Lagoon defendants at San Quentin State Prison.
In 1944, an appeals court overturned the convictions, finding there was no evidence that any of the young men had been involved in the killing.
Decades later, in 1981, McGrath would tell a Los Angeles Times interviewer that the successful appeal was "the most important event in my life. If I had never done anything since . . . my involvement in Sleepy Lagoon would justify my existence."
Born Alice Greenfield in Calgary, Canada, on April 5, 1917, McGrath moved with her family to Los Angeles when she was 5. Her parents were Jews who had fled Czarist oppression in Russia.
As the daughter of the only Yiddish-speaking foreigners in her poor southwest L.A. neighborhood, she would later say that she understood the experience of being "the other."
At various times in her life, she was a candy factory worker, an artists' model and a sales representative for Grove Press, the avant-garde publisher where she took a job after her second husband, poet Thomas McGrath, was blacklisted during the McCarthy era.
Later, with her third husband, Bruce Tegner, she co-wrote books on martial arts and taught women self-defense. She held a brown belt in judo.
But it was as a volunteer that McGrath continued to have a social impact. In 1984, she visited Nicaragua to experience the Sandinista regime after the defeat of the Somoza dictatorship. And over the following decades, she would make 86 trips to the embattled country, taking farmers, lawyers and doctors to meet with their counterparts.
She helped get medicines for Nicaraguan hospitals, and after Hurricane Mitch in 1998, she raised funds for the homeless.
In Ventura, where she moved from L.A. in 1970, McGrath started a pro-bono legal aid program for low-income families.
"People say I'm an optimist," she said in a speech in 2006. "I'm not. I'm a cheerful pessimist."
When Valdez visited to research his play, McGrath introduced him to the former defendants and their families, and shared her papers, including letters back and forth from San Quentin, that are stored at UCLA.
"She was the heart line of my story," Valdez said. "She maintained contact with 'her boys,' as she called them. She was a selfless person, with compassion and humor."
Three weeks ago, when he paid her a visit in Ventura, he said, "She was 92 years young. She was vibrant." And when Valdez mentioned his own upcoming 70th birthday, "her eyes opened wide and she laughed and said, 'Oh, to be 70 again!' "
McGrath is survived by a sister, Claire Jampol of Los Angeles, as well as by her daughter and a son, Daniel Schechter of Spokane Valley, Wash., both from her first marriage with businessman Max Schechter. Her first two marriages ended in divorce, and her third husband died in 1986.
The family is holding a private burial. A commemorative gathering will be planned.