Bertha JENSEN

Hi... I'm looking for information on the family of Bertha JENSEN. The information I currently have is based on a combination of census data, marriage & death records. She was likely born in Christiana in Oct. ca. 1858 (place is from her death information) Her father's name was Nikolai and her mother's name was Helene. (from her marriage record) She married Peter Nils Peterson in Chelsea, Massachusetts in 1889. I've search in the Norwegian Census data( http://www.rhd.uit.no/folketellinger/folketellinger_e.aspx) and can not seem to find any variation of the name Bertha listed with either parent who's name might some variation of Nikolai and Helene. Is there someone who might point me in the right direction, or give me some addtional advice on where to go next? Thanks, Linda