Unfortunately, you have a family story and you have a gun whose facts do not agree with the story.
Uberti is an Italian manufacturer best known for reproductions of historic US firearms, beginning with the Civil War Centennial in the early 1960s.
Hawes was an importer of various European firearms in the 1950s and 1960s.
What you have is a modern reproduction of the Sharps 4-barrelled derringer, and nothing that would have been available to your Grandmother ca 1920.
Those little guns were quite common while I was in highschool and college (I am your age +2) but should not be mistaken for originals.
Obviously Grandma was more active in guns than you thought.
Be interesting to see what she really had in her younger years.