Notes:

Lived in Montreal according to Library/William Greig/Item 2.

Unmarried and living with parents in Baltimore in 1922 according to father's obit (Library/William Greig/Item 7)

William Cowan repeorts from 1920 Census and other sleuthing:
"Margaret is listed as a music teacher and for employment as “Own Account” as opposed to employee. Presumably she gave private music lessons, perhaps to kids after school."
"Margaret lived with her parents at 2000 Madison Avenue. The US census of 1910 shows a Margaret Greig as a student nurse at Johns Hopkins Hospital at age 32. She, along with at least a page worth of others are shown as boarders at the hospital. We can be certain that this is “our” Margaret because it says she is Canadian and immigrated in 1907 and is of Scottish parents – the same info as is evident when she is living at 2000 Madison Avenue for the 1920 census.
"Given what I next found (1928 City Directory), the stint as a self-employed music teacher as reported in the 1920 census may have been a hiatus from nursing. Specifically, the 1928 US City Directory for Baltimore shows Margaret Greig and Elizabeth M Greig at 1701 Madison Avenue Apartment 4A. The directory lists them both as nurses. If indeed they were practicing nurses, there are three hospitals within walking distance of their apartment the closest being the University of Maryland Medical Centre a 15 minute walk away. Whether it was constructed back in 1928, I do not know."
"Interestingly, Margaret died in Vancouver, BC. This was on February 20, 1945. While I have not read the actual entry on page 15 in the Vancouver Sun of February 21, 1945 because I am not prepared to pay a fee to access it, I do know that it refers to her sister Elizabeth....... The access point through Ancestry.ca says “Residence 974 West 12 m Avenue”. What the “m” is all about, I do not know.