I think it would depend on a lot of things. Like, it'd be fine to feel angry, and I probably would be a little bitter, but then you have to ask yourself, are you bitter because someonee's publishing fanfic of your work, or are you bitter because it's making money? Like, I've seen fandoms where people are more interested in the "big name" fanfictions than the original work and think the original is going in a direction they don't like, so "X's fanfic is canon now". Would you still be bitter that someone's more popular than you with your stuff if they weren't making money off it?
It also depend how much they took your stuff for a fanfic. 50 Shades follows Twilight pretty closely and the characters are pretty recognisable (and that's if we ignore the allegations of plagiarism from other fanfic and her latest being also recognisable). After and real person fanfic, which is just writing down your fantasy about your crush and publishing it, it can be a bit creepy, but people are inspired by people all the time, they're just not so blatant about it. And then there's things like the Mortal Instruments, which may or may not actually be Harry Potter fanfiction, (it's complicated and would take too long to explain) but is wildly different enough that unless you were around at the time, or watch a lot of youtube, you wouldn't actually know (and maybe because she knows how to use an editor).
But either way, you might have to appreciate that they got something you didn't. Things are popular for a reason, and it's all very well to keep saying that fanfic isn't very good or that it's bad because it's not totally original, but if it's popular, it's clearly got something and denying that isn't going to help you at all.