A family tree on the internet lists this person as adopted.
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Ella married her sister Mary's husband (after Mary's death)
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Nebraska State Journal, Lincoln, NE, 6 Mar 1946
Deaths
KINCAID - Ella Sheldon Kincaid, died in Denver. Services 11 a.m. Thursday at Wadlows, Dr. Walter Aitken officiating. Wyuka.
[S2] 1900 Census.
Name: Ella Sheldon
Home in 1900: South Omaha Ward 1, Douglas, Nebraska
Age: 29
Birth Date: May 1871
Birthplace: Nebraska
Race: White
Gender: Female
Relationship to Head of House: Sister-in-law
Father's Birthplace: Ohio
Mother's Birthplace: Ohio
Marital Status: Single
Residence : South Omaha City, Douglas, Nebraska
[S16] Newspaper Article.
Nebraska State Journal, Lincoln, NE, 6 Mar 1946
Deaths
KINCAID - Ella Sheldon Kincaid, died in Denver. Services 11 a.m. Thursday at Wadlows, Dr. Walter Aitken officiating. Wyuka.
[S54] Cemetery Records Online, Wyuka Cemetery, Lincoln, Nebraska (Reliability: 3).
Kincaid, Ella Sheldon Sec-26 Lot-5999 Sp-5
Kincaid, Mary J. Sec-26 Lot-5999 Sp-9
Kincaid, Warren E. Sec-26 Lot-5999 Sp-8