Throughout her career as a solo artist, Stefani has won several music awards, including one Grammy Award, four MTV Video Music Awards, one American Music Award, one Brit Award, and two Billboard Music Awards. With No Doubt, she has won two Grammy Awards. In 2005, Rolling Stone called her "the only true female rock star left on radio or MTV" and featured her on the magazine's cover. Stefani received the Style Icon Award at the first People Magazine Awards in 2014. Additionally in 2016, the singer was honored at the Radio Disney Music Awards with a Hero Award, which is given to artists based on their personal contributions to various charitable works.  Stefani has been referred to as a "Pop Princess" by several contemporary music critics. In 2012, VH1 listed the singer at the number thirteen on their list of "100 Greatest Women in Music". Stefani's work has influenced a number of artists and musicians including Hayley Williams of Paramore, Best Coast, Katy Perry, Kesha, Marina and the Diamonds, Stefy, Rita Ora, Sky Ferreira, and Cover Drive. The latter group, a quartet of Barbados musicians, claimed that both Stefani and No Doubt had helped influence their music, to which the lead singer of the group, Amanda Reifer, admitted that she would "pass out" if she were to ever meet Stefani.  The lead single from Love. Angel. Music. Baby., "What You Waiting For?", was considered by Pitchfork to be one of the best singles by Stefani, and would later place it at number sixteen on their "Top 50 Singles of 2004" list. Additionally, "Hollaback Girl" from the aforementioned album would go on to be the first song to digitally sell an excess of one million copies in the United States; it was certified platinum in both the United States and Australia, and peak at number forty-one on Billboard's decade-end charts for 2000-09. Since its release in 2005, "Hollaback Girl" has been called Stefani's "signature song" by Rolling Stone.

Answer this question "What was her biggest achievement?" by extracting the answer from the text above.
Stefani has been referred to as a "Pop Princess" by several contemporary music critics.