Casals was born in 1948 in San Francisco to parents who had immigrated to the United States from El Salvador.

[1] When the children grew older, Manuel Casals took them to the public tennis courts of San Francisco and taught them how to play the game.

[citation needed] Casals also became involved in World Team Tennis, and she played with the Detroit Loves in 1974, the Los Angeles Strings from 1975 through 1977, the Anaheim Oranges in 1978, and the Oakland Breakers in 1982, before serving as the player-coach of the San Diego Friars in 1983.

[6] With Billie Jean King, Casals challenged the large difference in prize monies awarded to male and female players.

In 1970, Casals and other women threatened to boycott the Pacific Southwest Championships if they were not paid higher prize money and not given more media attention.

Since 1981 she has been president of Sportswomen, Inc., a California company she formed to promote a Women's Classic tour for older female players.

In 1990, she again teamed with Billie Jean King, this time to win the U.S. Open Seniors' women's doubles championship.

Casals was originally seeded 14th for the 1978 Wimbledon Championships, but a knee injury forced her withdrawal before the draw was made[13]