Depending on how you want to define it, I've seen some say this to be true for Summer Glau, crazy people, or semi crazy people. I honestly don't see it, but maybe I am biased.
Cameron Phillips (
Terminator: The Sarah Connor Chronicles) was anything but crazy. She was a cunning, hardcore killing machine. Eccentric, yes, but dangerously rational. Profoundly different from River Tam, an innocent teenage girl who'd been driven mad by the things that had been done to her. Or from Bennett Halvorsen (
Dollhouse), a shy, neurotic, ruthless scientific genius. True, there are points of commonality among her characters, but you could say the same for the repertoire of most any actor, since actors tend to get cast based on their suitability for a particular role. Really, the only Glau character who's particularly similar to River has been Tess from
The 4400. The proximity of those two roles in her career is presumably the source of the perception of typecasting, but her subsequent works have disproved the meme. The only thing Cameron had in common with River was fighting prowess, and Tess and Bennett didn't have that.