In 2001, Westbroek secured a 5-year contract as a company member of the Staatsoper Stuttgart. Her roles in Stuttgart included Carlotta (Schreker, Die Gezeichneten), Tosca, Emilia Marty (Janácek, Vec Makropulos, Desdemona (Verdi, Otello), Donna Anna (Mozart, Don Giovanni), Giulietta (Offenbach, Les Contes d'Hoffmann), Marie (Smetana, The Bartered Bride) and The Duchess of Parma (Busoni, Doktor Faust). In 2006, at the end of her work in Stuttgart, she was given the title of Kammersängerin der Staatsoper Stuttgart.
In 2003, Westbroek debuted at the Salzburger Festspiele as Agave in a concert performance of Egon Wellesz' Die Bakchantinnen. In 2004, she debuted at the Opéra Bastille as Madame Lidoine in Poulenc's Dialogues des Carmélites. Her debut at De Nederlandse Opera was as Katerina Izmailova in Shostakovich's Lady Macbeth of Mtsensk. This performance was commercially recorded for DVD release, and Westbroek won first prize from the Dutch VSCD Classical Music in the category "most impressive individual artistic achievement" for this performance. She repeated this role in her debut at the Royal Opera House, Covent Garden in London in October 2006. In 2008, she won the Grand Prix Antoine Livio of the Presse Musicale Internationale.
In her first world premiere production, Westbroek created the role of Anna Nicole Smith in the February 2011 Royal Opera premiere of Mark-Anthony Turnage's opera Anna Nicole at Covent Garden.
Westbroek made her Metropolitan Opera debut on April 22, 2011 singing the role of Sieglinde in the premiere of a new production of Wagner's Die Walküre directed by Robert Lapage.
Westbroek's commercial recordings include Bohuslav Martinu's Julietta, in the title role, for VMS Music Treasures, and three productions of Wagner's Die Walküre as Sieglinde with Bayreuth, Frankfurt, and Aix en Provence on CD and DVD. She is also featured in a DVD recording (Opus Arte) of Puccini's La fanciulla del West as Minnie, her own acknowledged favourite role.
Other recentlly released DVDs include Anna Nicole, Elektra from Strauss at the Salzburger festspiele 2010 and the role of Georgetta in il Tabarro in Puccini's Trittico.
Westbroek is married to tenor Frank van Aken.
