Valletta got her start in the fashion industry when her mother enrolled her in modeling school at the age of 15 at the Linda Layman Agency. Valletta, along with the likes of Kate Moss, Eva Herzigová, Tyra Banks, Carolyn Murphy and Shalom Harlow, was one of the most recognizable faces of the generation immediately subsequent to the original supermodels. During the 1990s she appeared 13 times on the cover of American "Vogue", second only to Claudia Schiffer's sixteen. Valletta was presented on the November 1999 Millennium cover of American "Vogue" as one of the "Modern Muses".