I can see that distinction. I know next to nothing about copyright law, although I gather that it's different in the UK and US (not that that is relevant in this case, because her books have publishers each place). I have a better grasp of plagiarism, but I think you're being generous with your example - if the hypothetical person is basing something on your work (re-worded and supplemented), I think it would still need attribution. Or a big thank-you
in some sort of acknowledgment section, anyway.