I don't have any problems with someone changing fanfic to original fic. With, for example, 50 Shades, the "fanfic" was so different from the source material that filing serial numbers off was all that was needed. (It's still shit, but not because it's fanfic.) Lois McMaster Bujold is one of my favorite authors and she started with Star Trek fanfic that she changed to something else. But that's the important part: she changed it. She was inspired by another source, and if you know that you can see where it came from, but she used that inspiration to make her own characters, plot, and setting.

Cassandra Claire's a different matter. She pulled all these plot elements and characters from different places and threw them together in a weird mishmash. All she did was file the serial numbers off, but she didn't make anything of her own. Her fanfic was like this too, from what I can gather. And I don't think the excerpts I've seen from her fic that are not plagiarized from Pamela Dean are well-written anyway.