She played several guest roles in TV shows like Baantjer, Intensive Care, De Band, Meiden van De Wit and Kinderen Geen Bezwaar. She also hosted Staatsloterij Live and the Dutch version of Idols. Janzen played several parts in movies: De Dominee, Feestje, Deuce Bigalow: European Gigolo, Volle Maan, Alles is Liefde, Kicks and the made-for-TV film Loverboy. In December 2002 her single “Achter De Sterren”, the title song from the movie Science Fiction was released.

Janzen won the John Kraaijkamp Musical Award in 2002 for Upcoming Talent for her lead in Saturday Night Fever. She also won a musical award in 2005 for Best actress in a supporting role for the musical Crazy For You. She got nominated for Best female lead in 2006 as Belle in Beauty and the Beast and in 2007 she got nominated for the same prize for her role as Jane in the musical Tarzan. Because of her pregnancy she had to temporarily leave her part in the musical Tarzan from September 2008 through April 2009. She was replaced by Bente van den Brand. After Tarzan she played a part in the Disney Musical Sing-Along. In 2010 Janzen can be seen in the musical Petticoat. It’s an original Dutch musical, written especially for her. After her role in Petticoat she played the role of Glinda in the Dutch rendition of the Broadway musical Wicked.

Janzen is in a relationship with Marco Geeratz. She gave birth to their first son, James, on January 23, 2009. On December 15, 2014, they were married in London. Geeratz has three children from a prior relationship. On March 30, 2018, the couple had their second son, Bobby.

In 2011 Janzen ended her contract with the Dutch TV channel AVRO and signed a contract with RTL. According to her, hosting the Award shows she had been hosting at the AVRO for the fourth year in a row, would make her performance look cheap. She was enthused by the idea of experiencing other things. In 2012 Janzen had roles in the series Divorce and Goede tijden, slechte tijden. Later on in 2019 Janzen returned in another small role in Goede tijden, slechte tijden.

In 2019 Janzen was one of the members of the “Wall of the World” in the American television show The World’s Best. On 4 December 2019, she was announced one of the three presenters of the Eurovision Song Contest 2020 in Rotterdam alongside Edsilia Rombley and Jan Smit.