This entire kerfuffle did inspire me to actually look up the text of US Copyright law, just for the hell of it. Not that that really has any bearing here anyway.

I think if the OP doesn't want their story to be played with, then forbid all remixes. You can't allow it in some instances and not others and oh, btw, the OP does realize that their fan fiction is in essence a "remix" of the original works?

Oh and if you're not sure what I would feel comfortable with, next time do NOT hesitate to ask me, hon. I'll tell you straight up either way.