Christine Sundby, Nordby or Christoffersdatter

I'm have trouble finding the parents of my great grandmother Christine. She was born in Norway in 1868 and emigrated to Minnesota in 1888 where she married Peter Olson Sjol. I found her maiden name listed on the death records of some of her children. Some list it as Sundby, some say Nordby and one says Christephersen. Peter was born in 1860 and emigrated in 1882- If anyone can be any help I would greatly appreciate it.