Thank you. There were a couple of possibilities for James and Mary in manifests but none are right.
However, I did see these Winnipeg census entries and wondered if it could be Mary widowed and living nearby to her daughters:
1916
www.familysearch.org/ark:/61903/1:1:KMG1-1CM1921 Can't see it on Family Search, but from elsewhere:
Mary Donaldson, 58, widowed, head of household. Showing as Housekeeper with a number of people lodging at the property
Parents Scottish
Year of Immigration 1913
Winnipeg (City) Manitoba
1926
www.familysearch.org/ark:/61903/1:1:QPVP-27PBThe ref to year of immigration is what made me look at the shipping manifests again. Can't see anything suitable for her so far though to help with whether it is her or not

Monica