It may be that John & Annie (Kelley) Keller had other children. Check this out, a possible daughter Anna Marie:
"Ohio, County Marriages, 1789-2013," database with images, FamilySearch(https://familysearch.org/ark:/61903/1:1:XDKB-WMD : 8 December 2014), John Keller in entry for Chas E Christian and Anna Marie Keller, 04 Jun 1908; citing Stark, Ohio, United States, reference p 559; county courthouses, Ohio; FHL microfilm 875,630.
Also, your Mary's death record says both her parents were born in Ohio. That is long after the fact, however!
"Ohio Deaths, 1908-1953," database with images, FamilySearch(https://familysearch.org/ark:/61903/1:1:X82R-1LH : 8 December 2014), John Keller in entry for Mary Dillon, 01 Jan 1920; citing Cincinnati, Hamilton, Ohio, reference fn 2688; FHL microfilm 1,984,987.
Hope this helps! -NGP