Were they trying to make money selling fanfic set in her universe? That would be different, and I wouldn't have a problem with her suing them for that. But when I think of fanfic I think of writing which is non-commercial rather than for-profit.
There was nobody trying to sell their Pern fanfic when I was in. But one still had to follow the author's rules. If anyone was violating those rules, a cease-and-desist was usually enough to stop it. If she actually sued someone, it would have to be for something really serious. But I never saw that happen, and can't speak to what may have gone on in the recent past.
I still miss the fanzines run by grownups who didn't develop swelled heads. They were few and far between.
Usually egoboo took over, and, like Gresham's law, bad zines drive out good.