Gena Oleson 1886-1906

Looking for information on a relative. Gena Oleson was my great great grandfathers, Bernt Andersons, illegitimate daughter. I have been told he had an affair and Gena was a product of that affair. My family settled in Sauk county Wisconsin, but at the time of my gr gr grandfather's death, he was in Faulk South Dakota. They are all buried together,(including Gena) in Sauk County, Wisconsin at Big Hollow Cemetery. Im just trying to piece together who Gena's mother her history. She died young (20) so I dont know what I may be able to find on her. i dont know if she was from Wisconsin, South Dakota or maybe somewhere in between.