You could always tell her that there are worse parts of fandom. My ex-roommate was into fandom as well, but she and some of her other fandom friends would talk on the phone and role play it. Now, normally, I have no issues with RPing (another friend and I used to do it too, though she would never admit that what we were doing was basically scripting fanfic), but she and these friends (who all tended to be 16-18 year old girls) would role play yaoi (slash) Kingdom Hearts (anime/video game) scenes where they were basically seducing one another. And they would meow at each other. It was creepy.

But, yay for maybe writing a story! Even if you don't finish (or start) it, sometimes just working through the plot and figuring things out is enough to get other creative juices flowing.