I have a sister of my great-grandfather that I haven't found.
Jessie Nicoll was born 28 Dec 1893 in Dundee, Scotland to John Nicoll (1860-1902) and Margaret Buist (1856-1917). She arrived in the US in 1909, resided with family members in Andover, Mass until 1920, when the city directory said "rem from town".
This appears to be her in the 1920 census with her brother Andrew in Minnesota -
https://familysearch.org/ark:/61903/1:1:MW1Q-BPD Andrew appeared to use the spelling Nicol instead of Nicoll. There is a boy below Jessie that is listed as a grandson, but Andrew didn't seem to have any children of childbearing age, so I wonder if it was really Jessie's son.
I couldn't find her in 1930, but there are entries for Jessie Nicoll in the 1936 & 1939 St. Paul city directories that may or may not be her.
There was an entry in the SSDI for a Jessie Blake with the same birthday, but the Mass. death index had her born in Massachusetts, so it may be someone else.
I have found most of the rest of the family. Her brothers David & George died in 1917 & 1919 respectively. There is a sister listed as Mrs. James Anderson of Scotland in David's obit, but I have never figured out her first name. Jessie was listed as living in Andover, Mass. in David's obit.
Her brother Thomas died in Carnoustie, Scotland in 1958. Brother Andrew died 7 Feb 1978 in Minnesota, but his obit didn't mention her. Brother John died 2 Sep 1955 in Los Angeles. Brother William died 27 Feb. 1966 in Augusta, Maine.
I never found anything further that was revealing about her or the possible son in the 1920 census, so I need another set of eyes. Thanks!