I'd be interested in hearing the case for ISFP over ISTP. I mean, I guess the Fi would explain her seemingly severe self-consciousness and "moody" characterization (which I don't personally see, but I guess people react badly to her stone face + seriousness combo), but I still think she has more of a T vibe.
She's been called "quietly intense," "intimidating," "fierce," and "tough" by people who have worked with her, and these are all things that I'd quicker associate with ISTPs than ISFPs. That fucking guy from Twilight (the one with the big alien-looking head that all the little tweens cream their pants over) even said that he was surprised that she was playing the girl (whatever the name is...I forget that, too) because she was so different from the book version. He said something about her being "tougher" and "stronger" than the "damsel-in-distress" girl in the book. Also, Joan Jett - who she played in that "Runaways" movie - has said that Kristen is strangely similar to her (and so have reviewers for that film...though I haven't seen it myself.) And Joan Jett is no F.
Apparently she is also notorious for being foul-mouthed and kind of crude. All screams ISTP to me.
In any case, I'm bored right now and she kind of intrigues me. I always kind of ignored her because of my distaste for anything having to do with Twilight, but this thread has got me interested, so...