It's one thing to be inspired by someone else's story, a book, a movie, a TV show, or whatever. As long as you put your own spin on the idea and write it in your own way, it's fine. No idea is truly original. It's when you're literally copying or paraphrasing someone else's words without crediting them that you're plagiarizing. I don't see how anyone can do that and think it's okay.
That's so weird that someone would ask if she could copy your story, Steph LOL. I mean, at least she asked instead of just doing it, but why would she want to do that in the first place? Just write your own words!!