Melissa Bright was still alive in 1870:
"United States Census, 1870," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MFSH-LW9 : 12 April 2016), Melissa Bright in household of Caleb Bright, Mississippi, United States; citing p. 26, family 15, NARA microfilm publication M593 (Washington D.C.: National Archives and Records Administration, n.d.); FHL microfilm 552,219.
In fact, she seems to have been counted twice. Here she is with Susan:
"United States Census, 1870," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MFSH-KXK : 12 April 2016), Malissy Bright in household of Caleb Bright, Mississippi, United States; citing p. 8, family 17, NARA microfilm publication M593 (Washington D.C.: National Archives and Records Administration, n.d.); FHL microfilm 552,219.