Horton was born in Japan and educated in California at Bonita Vista High School and San Diego State University.

She served as mayor until she was term limited in 2002, and ran for a seat in the California State Assembly from the 78th district.

Shirley Grasser Horton was born in Japan while her father was serving in the United States Navy.

[10] Horton was appointed in 1991, out of twenty-seven applicants, by a unanimous vote to the Chula Vista city council to fill the vacancy created by Tim Nader's becoming mayor following the death of Mayor Gail McCandliss.

[12][13][14] On February 14, 1994, Horton announced that she would seek the mayoral office of Chula Vista and placed first out of four candidates in the election after spending $67,422 during the campaign.