Mezue ahịrịokwu na-esonụ: N'egwuregwu Olimpik nke Oge Ezumike nke 2008 na Beijing, Jansen gbasawanyere usoro igwu mmiri ya gaa n'ihe omume abụọ: 200-mita freestyle na 4 × 200-mita freestyle relay. O wepụrụ oge ntinye FINA B nke 2:02.20 (200 m freestyle) site na Danish Open na Copenhagen. Na 200 m freestyle, Jansen gbara ọsọ gaa n'ọnọdụ nke anọ na nke iri atọ na anọ n'ozuzu ya n'otu okpomọkụ dị ka Athens site na otu sekọnd n'ihu Lynette Lim nke Singapore na 2:01.30. O sonyekwara Hjorth-Hansen, Micha Østergaard, na Lotte Friis na
4 × 200 m freestyle relay. Na-egwu mmiri na ụkwụ nke atọ, Jansen dekọtara nkewa nke 2:00.31, ndị otu Danish mechiri ọkụ mbụ na nke iri n'ozuzu ya na ndekọ Danish nke 8:00.81.