I think she died before the 1920 Census.
1920 Cedar, Mineral, MT
H. C. Hopkins, b. OH, 57, widower, section foreman railroad
The Missoula Public Library's Audra Browman Research Room, www.missoulapubliclibrary.org/montana-collection
has material regarding Mineral County but their web site doesn't say they do research.
I'd contact the Montana State Genealogical Society/Lewis & Clark Genealogical Society, www.rootsweb.ancestry.com/~mtlcgs/index.htm
and ask if they have an obituary for a Hopkins. Successful Searching & Happy New Year!