The Verdict: Need More Info
If she is living, she can become Canadian by sending the Minister a written election. If she has died, her descendants should take the citizenship by descent quiz.
Before 1947 a woman could cease to be a British subject only because she married a foreigner, or because her husband took another nationality. If she would otherwise have been a citizen under the 1946 Act, she acquires citizenship as soon as the Minister receives her written notice. There is no residence requirement, no permanent residence and no test.
She married before 1947, so she would be in her nineties at the very least today, so this is more often reached through her children and grandchildren. If she counts as Canadian, they may have been born to a Canadian mother.
Documents to find: her marriage certificate, her own birth or naturalisation record, and the birth records of each generation below her.