Lewis's clients include Miguel, Gwen Stefani, Rihanna, Courtney Love, Britney Spears, Colbie Caillat, Linkin Park, Demi Lovato, Tyson Ritter of The All-American Rejects, The Pussycat Dolls, Bryson Tiller, Iggy Azalea, and Jack Black.

Lewis has taught voice classes and lectured at the Liverpool Institute for Performing Arts, University of California, Berkeley, Musicians Institute in Hollywood, Blue Bear School of Music, Santa Monica College, National Academy of Songwriters, and UCLA.

[5][better source needed] Lewis appeared as vocal coach on CBS’s Rockstar: Supernova and MTV’s Rock The Cradle.

[6] She has also appeared as a commentator on TV Guide Network’s Idol Chat,[7] VH1’s Dice: Undisputed, and Miss America: Reality Check.

[9] Both books not only focus on exercises and information to train his/her voice, but expand upon the challenges that professional singers face.