Gail Zappa, the widow of the rock guitarist and composer Frank Zappa, who battled major record companies and cover bands alike as a fierce steward of her husband’s musical legacy, died on Wednesday at her home in Los Angeles. She was 70.

Her death was announced by her family, which did not disclose the cause.

Mrs. Zappa met her future husband in 1966, when she was a 21-year-old secretary at the Whisky a Go Go nightclub in Los Angeles. He was four years older and already establishing his reputation as a maverick musician with a bad-boy streak as the leader of the Mothers of Invention, which had just released its first album, “Freak Out!”

After meeting Gail, it took Zappa just “a couple of minutes” to fall in love with her, he said in his 1989 autobiography, “The Real Frank Zappa Book,” written with Peter Occhiogrosso. Her first impression had more to do with his casual hygiene. She also later recalled that very early in their relationship, Zappa had played his record collection for her and gauged her reaction.

“I didn’t know it was a test,” she said, “and he never told me that I passed.”

She soon moved in with him, and the couple were married in 1967, just as the Mothers of Invention were about to leave for a European tour.