Martha was born about 1841. She passed away in 1899.
Sources
"District of Columbia Marriages, 1811-1950," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:XL86-G88 : 4 November 2017), John L Mcduell and Martha A Hunter, 26 Apr 1860; citing p. , Records Office, Washington D.C.; FHL microfilm 2,079,252.
"United States Census, 1870," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MNW1-LHW : 12 April 2016), Martha A Mcduell in household of John L Mcduell, District of Columbia, United States; citing p. 155, family 1263, NARA microfilm publication M593 (Washington D.C.: National Archives and Records Administration, n.d.); FHL microfilm 545,623.
"United States Census, 1880," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:M6CC-FS7 : 24 August 2017), Martha A Mc Duell in household of John L Mc Duell, Washington, Washington, District of Columbia, United States; citing enumeration district ED 78, sheet 174D, NARA microfilm publication T9 (Washington D.C.: National Archives and Records Administration, n.d.), roll 0124; FHL microfilm 1,254,124.