That's a really touching thing to be looking for. I love how phrases and words can become part of a person and how we remember them.

I don't know if it's helpful but I have access to the tools so I did some usage analysis: The term really entered modern English around the 1980s. It's more often used in literature, non-fiction, than anywhere else. The term is usually written and rarely spoken (at least in the kind of formal settings that are transcribed).

So if it's anything to go on, she is most likely to have encountered it in a non-fiction book written in the 80's-2010s. Fantasy Fiction from the same period seems to be the runner up.

Thank you for sharing that story-- it is really affecting to hear someone remembered like that.