It has to be after Herbert died on March 12, 1947, when her husband died, because she is apparently listed as the executor on his death report.
http://"New York, New York City Municipal Deaths, 1795-1949", database, FamilySearch (https://www.familysearch.org/ark:/61903/1:1:2WGG-RCF : 3 June 2020), Alice McKinnon in entry for Herbert McKinnon, 1947.
There is an unsourced statement on ancestry.com that says she died in 1951, in Queens, New York, but I couldn't find any support for that statement:
https://www.ancestry.com/facts?_phcmd=u(%27https://www.ancestry.com/search/
P.S. As you get more over to Nova Scotia, you are getting closer to my McKinnon ancestors. We are going to be relatives yet.