I can find no marriage for Mary in Ashtabula, that would fit her, so it is possible that she died before getting married.
Not my line, just trying to help.
Lydia A. Morse md Curtis R. Waters on December 25, 1862 in Ashtabula Co., OH
1870 Erie Co., PA - Waterford Twp. - Waterford Borough - July 25, 1870 - page 19/524 167/167 Waters, C. R. 40 - school teacher - 1200/400 - OH Adda 32 - keeps house - OH Minnie F. 7 - OH Nina 5 - PA
1880 Trumbull Co. OH - West Farmington - ED# 189 - page 19/524 167/167 Waters, Curtis R. head - 43 - M. E. Minister - OH ?? CT Lydia A. wife - 39 - keeps house - OH NH NY Minnie dau - 16 - school - OH OH OH Nina A. dau - 14 - school - OH OH OH George D. son - 6 - school - OH OH OH
1900 Lake Co., SD - Madison Twp. - ED# 216 - June 5, 1900 - page 5B 1200 10th Street 87/98 Waters, Curtis R. head - Septembrrr 1835 - 64 - md 38 yrs - OH CT MA - teacher Lydia A. wife - May 1841 - 59 - had 4 children/4 living - OH NH MA Bessie (Elizabeth) dau - December 1881 - 18 - single - Iowa OH OH - at school
1016 North Avenue 89/102 Waters, George D. head - February 1873 - 27 - md 0 yrs - OH OH OH - teacher Ida L. wife - October 1871 - 28 - had o children - Iowa NY Wales - teacher
1900 Lake Co., SD - Madison - ED# 216 - June 6, 1900 - page 7B Normal Dormitory Waters, Nina A. matron - May 1866 - 34 - single - OH OH OH - normal matron
1910 Lake Co., SD - ward 1 - Madison - ED# 269 - April 15, 1910 - page 1B Waters, Lydia A. head - 68 - widow - OH NH NH - own income Elizabeth dau - 27 - single - OH OH OH - teacher/public school Nina A. dau - 43 - single - OH OH OH - matron/state dormitory