Kristen Stewart talked about Joan Jett in a recent interview about The Twilight Saga: New Moon from November 7th (written by Christina Radish):
Q: How did you balance playing Bella with playing a character like Joan Jett?
Kristen: I can only play characters that I feel like are real people, in a complete way, and in such a whole way that, if I fake any aspect of it, I will have failed them and, literally, they’re slaughtered. It’s like they don’t exist anymore, unless I do it. So, in terms of approaching parts, it just happens.
I got to know Joan, not only as her now, but also through footage and the script and story. I feel like I got to know who she was, in such a whole way that it’s not about imitating, even though I was really concerned about details being right, like gestures and stuff. I really wanted to do a good impersonation, but I also didn’t want it to be imitation. I wanted it to be natural.
Playing Joan Jett had nothing to do with Bella. It was a small period of time that I had to do it, but it was an opportunity that I jumped on because it was going to go away if I hadn’t. I would’ve liked more time.
You can read the rest of the interview HERE.