This might be your Marie if she didn't re-marry after Arlo's death.
A Marie V. White b. 21 Feb 1931, Last Residence=Nampa, Canyon Co., ID died 11 July 2003. Her soc. sec. # was assigned in Idaho before 1951. Source: Social Security Death Index.
You'll need a copy of her obituary to figure out if this Marie was your Marie. You can find an obituary volunteer at Random Acts Genealogical Kindness. Go to raogk.org, read guidelines, choose Idaho, choose Shoshone Co. and one obit volunteer.
Also the Caldwell Public Library, firstname.lastname@example.org
has an obituary service. Successful Searching!