need some help

I've located the parents of Johan Halvorsen, but I'm not sure how to begin with his wife Mathia since she's from Olso. How would I begin to find church records or family history for her? 1865 Norway Census Municipality: Kristiania Town Quarter: Gamle Akers Menighed Street: Maridalsveien House owner: Anders Gulbrandsen Number of persons in this domicile: 28 • Johan Halvorsen, father of the house, married, canvas worker, born 1839 at Næs Romerige (now Nes, Romerike) • Mathia Martinsen, his wife, married, born 1840 at Christiania • Carl Gustav Johansen, their son, single, born 1865 at Christiania