She was born October 1879 per 1900 census. She appears on the (14 June) 1880 census, indicating she is 7/12 old, born in October. Find a Grave and the grave marker says she was born 16 Oct 1880.
Sources
"United States Census, 1880," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MZXP-G4R : 8 September 2017), Olive L French in household of Hiram H French, Victor, Ontario, New York, United States; citing enumeration district ED 139, sheet 509B, NARA microfilm publication T9 (Washington D.C.: National Archives and Records Administration, n.d.), roll 0909; FHL microfilm 1,254,909.
"United States Census, 1900," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:M9VJ-ZGT : accessed 23 November 2017), Olive L French in household of Elvina French, Verona, Lamoure, Cottonwood, Lake View & Ovid Townships & Schools Lamoure village, LaMoure, North Dakota, United States; citing enumeration district (ED) 82, sheet 10B, family 165, NARA microfilm publication T623 (Washington, D.C.: National Archives and Records Administration, 1972.); FHL microfilm 1,241,229.
"United States Census, 1900," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MM51-R1W : accessed 15 May 2021), Olive French in household of William Allen, Aberdeen city Ward 4, Brown, South Dakota, United States; citing enumeration district (ED) 45, sheet 8A, family 142, NARA microfilm publication T623 (Washington, D.C.: National Archives and Records Administration, 1972.); FHL microfilm 1,241,546.
"North Dakota Census, 1925," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:QVRM-BGM9 : 17 March 2018), Olive L Frederick in household of Henry L Frederick, La Moure, La Moure, North Dakota, United States; citing sheet number 1, family number 2, State Historical Society of North Dakota; FHL microfilm 1,731,399.
"United States Census, 1940," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:KQGP-WJK : 15 December 2019), Olive L Fredericks in household of Charles B Baldwin, West Bloomfield Town, Ontario, New York, United States; citing enumeration district (ED) 35-68, sheet 11B, line 55, family 228, Sixteenth Census of the United States, 1940, NARA digital publication T627. Records of the Bureau of the Census, 1790 - 2007, RG 29. Washington, D.C.: National Archives and Records Administration, 2012, roll 2707.
Find a Grave, database and images (https://www.findagrave.com : accessed 05 May 2020), memorial page for Olive Lavina French Frederick (16 Oct 1880–7 Mar 1979), Find A Grave: Memorial #111229422, citing Boughton Hill Cemetery, Victor, Ontario County, New York, USA ; Maintained by Ralph Baldwin (contributor 49365797) .
Obit: Democrat and Chronicle (Rochester, New York) · 8 Mar 1979, Thu ·Page 15
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