I wonder if this could be her death record from 1921 in Fergus Falls, Minnesota:https://familysearch.org/pal:/MM9.1.1/FD38-74B
Looks like a son Oliver also lived in Fergus Falls on the 1930 census. She is also listed in the Minnesota Death Index and you could send for a copy of that.
There is also a Selena Froslie in the Alien Registration records. http://www.mndiscoverycenter.com/research/
I see they have a daughter Selena and don't know if this is the same one. If it is the right one, she would not have been born in the United States, and possible the marriage took place in Norway.
Hope this info may help