Searching for parents of Danish grandmother

Anna Dorthea Rasmussen was born on the 28 September 1869 in Stokkemark, Lolland, Denmark.  They emigrated to the USA in about 1872 or 73.  She is listed in 1880 census of Campbell, Wilkin County, Minnesota, USA as the eldest child of Lars and Hannah Rasmuson.  I would like to know more about her parents including her mother's maiden name.