mendoza was born on december 22, 1934 in the city of fillmore, california to parents tiburcio and margarita magdalena. her parents had fled mexico after losing their family farm. mendoza was the oldest of five children and had two younger brothers and two younger sisters. she was born in fillmore while her father worked as a labor organizer in the sespe ranch, a large ranch in the city. there he helped organize citrus fruit and avocado pickers. mendoza's father helped the ranch workers go on strike and demand better working conditions and wages.