Kammala wannan jumla: A Wasannin Olympics na 2008 a Beijing, Jansen ta fadada shirinta na yin iyo zuwa wasanni biyu: mita 200 mai kyauta da 4 × 200 mita mai kyauta. Ta share lokacin shigarwa na FINA B na 2:02.20 (200 m freestyle) daga Danish Open a Copenhagen. A tseren tseren mita 200, Jansen ya yi tsere zuwa matsayi na huɗu da na talatin da huɗu gaba ɗaya a kan zafi ɗaya kamar Athens ta daidai da na biyu a gaban Lynette Lim na Singapore a 2:01.30. Ta kuma haɗu da Hjorth-Hansen, Micha Østergaard, da Lotte Friis a cikin
4 × 200 m kyauta kyauta. Yin iyo a mataki na uku, Jansen ya rubuta rabuwa na 2:00.31, kuma tawagar Danish ta kammala zafin farko a karo na goma gaba daya tare da rikodin Danish na 8:00.81.