Updated: Evelyn's profile was disconnected and is now reconnected to this family through her father (and to her spouse).
I came across the profile of Evelyn Stewart in this family while working on another profile. Clarification on her may help some with another connection path, if needed and depending.
In 1920, Frank Calvin Northrup, a grandson of Solomon Northup, married Eva Caty Stewart in Weedsport, NY. Eva later shows as Evelyn or Evelyn S. In 1925, she's living with Frank and daughter Mariline who is listed as 8 years and on their 1930 Census, Mariline is listed as 13 years old on the 1930 (may not be Frank's daughter). Evelyn is on another record as a servant and daughter is listed with her within that household. Later, Evelyn moves with her daughter to PA and she dies in Philadelphia in 1964 per her death certificate.
Daughter Mariline's Find a Grave is here with obituary which mentions her mother, not father, and Auntie Harriet Tubman.
I was going to connect Evelyn to Frank last night but I am now holding on adding Evelyn and her daughter after finding the profile for Evelyn under William and Emma.
The Evelyn who married Northrup was born May 12, 1890 in Canada per death record. Her father is listed as John I Stewart on her marriage and John Isaac Stewart on her death record. Her mother is listed as McNiel on marriage and Hollina H. McNiel on death record (Mariline was informant). Nothing found on Hollina. John may have married more than once and may have died about 1893 when Evelyn was very young. If her parents were not around she may have gone to live with her relatives. She did use the middle name Caty on her marriage.
Could she be the 6 year old Kate that is listed on the 1900 Census with T Harriet Davis and William Stewart and as the Evelyn listed with William and Emma later on?
There is a "Photographic postcard of Harriet Tubman's great nieces, Eva and Alida Stewart" here on the Smithsonian website, along with a news clipping after. She is listed next to the photo as Eva Northrup Stewart, American, 1890-1964.
(edited to add link to Frank)