Thanks, J.J.
I suspect it is Marion, if it's either of the sisters, as Hortense eventually went in for abstract painting after her career painting china, whereas Marion did landscapes.
What I know about the painting:
It is either a full-length or 3/4 portrait, a large canvas, about 2 metres high, 1 metre wide. It details a tall woman in dark clothes, with possibly a black shawl, carrying a leather satchel (like an old-fashioned doctors bag), standing against a backdrop of fields. She had strong features ("a face like a hatchet", to quote my mother). The frame was dark. The model was my great- great- grandmother, who emigrated to Canada in 1905 to join her daughter's family in Hamilton, and died in Hamilton in March 1928 (which gives a relative time period and points to a Canadian artist, possibly even someone resident in Hamilton, as the model lived in Corktown and worked in service). According to my mother, it was at the head of the stairs of the old AGH as you went in. (As a young woman, she used to go 'visit' with her when the family had errands in town.)
Either it was on long loan to the Art Gallery of Hamilton, or it has disappeared from their records, as I had the current curator have a look for it and she came up empty. What I will have to do, I think, is go down there for a face to face next time I'm back in Hamilton. I've contacted the Women's Art Association of Hamilton (which has been around since the late 19th c) to see if perhaps one of their older members remembers the painting. Then I'll comb the national salon reviews for the decade of the 20s for likely artists and descriptions of the painting. But it's all slow forensic spelunking. But I'd give my eye-teeth to see that painting. Great-great-gramma Hazell launched me into this whole family tree business, and I feel a connection across the generations to her.
Thanks, everyone, for all your help. Shall I mark this one completed?