John J. Maynard and Susie McDonald were married in Carroll County, Tennessee, 0n 4 Jan 1899.("Tennessee, County Marriages, 1790-1950," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:XZ7C-ZM9 : 11 February 2018), John J Maynard and Susie Mcdonald, 04 Jan 1899; citing Carroll, Tennessee, United States, Marriage, p. 100, Tennessee State Library and Archives, Nashville and county clerk offices from various counties; FHL microfilm 944,060.)
According to the 1900 US Census, New Concord, Calloway, Kentucky, Sue Maynard, wife of John J. Maynard and daughter-in-law of William Maynard, was born in Sept 1875 in Tennessee.("United States Census, 1900," database with images, FamilySearch(https://familysearch.org/ark:/61903/1:1:M9WK-914 : accessed 10 July 2018), John J Maynard in household of William Maynard, Magisterial District 2, New Concord, Calloway, Kentucky, United States; citing enumeration district (ED) 15, sheet 22B, family 420, NARA microfilm publication T623 (Washington, D.C.: National Archives and Records Administration, 1972.); FHL microfilm 1,240,512.)
Not sure if it is the correct Susan, but it might be worth exploring: A Susan Mc Donald, daughter of David and Elizabeth J. Mc Donald, lived in District 3, Carroll County, Tennessee, in 1880. She was 6 years old, the right age.("United States Census, 1880," database with images, FamilySearch(https://familysearch.org/ark:/61903/1:1:MDQP-YMF : 15 July 2017), Susan Mc Donald in household of David Mc Donald, District 3, Carroll, Tennessee, United States; citing enumeration district ED 10, sheet 33B, NARA microfilm publication T9 (Washington D.C.: National Archives and Records Administration, n.d.), roll 1246; FHL microfilm 1,255,246.)