It’s not like she even had to learn all the verses, just the first one.
It’s what, 7 short lines? She didn’t already know 7 short, (in)famous lines of a lyric sung in fecking Canada and around the world?
She filmed in Toronto for years. It’s the capital of Ontario, a province steeped in British history and culture.
But sure, how was she supposed to know anything about anything? I mean, who even knew Canada was in the Commonwealth, right? And that Britain had a monarch and a royal family, right? And that other countries had, like, these anthem things, right, that people like sung along to while not chatting away having conversations, right? Like medieval times.
She didn’t even have to sing. Standing respectfully is acceptable, as many overseas nationals, diplomats and republicans (small r) and others do at memorial events like Remembrance Day.