I wish I could show this to my father-in-law, but he’s in his 80s, speaks little English, and it would take a long time to even get the meme history built up with him to actually follow the humor. If I could get him to understand the humor, though, he’d probably love it; he taught this for decades at a university.
Maybe try a different password manager and see if its interface is easier for her to use? There are lots of options, not all of them FOSS but this might be a time to accept a well-regarded commercial solution. Or, since she has the iPhone, try using their password solution. They integrate that pretty thoroughly in their apps and OS, and I think with this year’s OS releases across the board they have turned it into more of a fully-fledged password manager with its own apps. I know very little about it, but there might be a way to integrate it with Firefox on desktop now.