From the NY Times obituary:
Their sound may have been commercial and safe, but early on their politics were somewhat risky for a group courting a mass audience. Like Mr. Yarrow and Mr. Stookey, Ms. Travers was outspoken in her support for the civil-rights and antiwar movements, in sharp contrast to clean-cut folk groups like the Kingston Trio, which avoided making political statements.
Peter, Paul and Mary went on to perform at the 1963 March on Washington and joined the voting-rights marches from Selma to Montgomery, Ala., in 1965.
Over the years they performed frequently at political rallies and demonstrations in the United States and abroad. After the group disbanded, in 1970, Ms. Travers continued to perform at political events around the world as she pursued a solo career.
“They made folk music not just palatable but accessible to a mass audience,” David Hajdu, the author of “Positively Fourth Street,” a book about Mr. Dylan, Joan Baez and their circle, said in an interview. Ms. Travers, he added, was crucial to the group’s image, which had a lot to do with its appeal. “She had a kind of sexual confidence combined with intelligence, edginess and social consciousness — a potent combination,” he said. “If you look at clips of their performances, the camera fixates on her. The act was all about Mary.”