As an amateur, Castillo was one of the most decorated women's golfers in the state of Hawaii, winning three
United States Golf Association (USGA) titles, the
U.S. Girls' Junior Championship in 1978 and the
U.S. Women's Amateur Public Links in both 1979 and 1980. In 1979 Castillo defeated
Becky Pearson 2 up, then edged Pam Miller 2 & 1 a year later. She is the youngest to hold two USGA titles simultaneously and only Hawaii golfer to win three USGA national championships, and one of only four golfers ever to hold two USGA titles simultaneously. She also won the Junior World title for the 13-14 year-old division in 1974. After graduating from
Kaiser High School in
Hawaii Kai, Castillo attended the
University of Tulsa, where she was a member of the team that won the 1980
AIAW National Championship title. After two years she transferred to
Stanford University, where she received a bachelor's degree in communication in 1983 and earned honorable mention All-American honors. She won the
Hawaii State Open Women's Golf Tournament in 1977 and 1983, then three times consecutively in 1993, 1994 and 1995, giving her a record five state titles. She is also two-time winner of the Hawaii State Women's Match Play Championship (1979, 1980) and the 1981 Hawaii State Women's Stroke Play champion. ==Professional career==