The name Ragnhild Sigurdsdotter may refer to two different figures from Old Norse literature, an amalgam of them, or a purely fictitious figure.
The wife of Halfdan the Elder
A woman who lived during the late 9th and/or early 10th centuries, who... Wikipedia
Great grandchildren: Harald Greycloak, Tryggve Olafsson, Sitric Cáech, and more
Grandparent: Helge
Grandchildren: Eric Bloodaxe, Haakon the Good, Bjørn Farmann, and more
Parents: Sigurd Hart
Children: Harald Fairhair