Here’s an article of Joan Jett talks about Kristen Stewart.
“So much happened. It’s hard to fit it all in, but the film definitely gives you a sense of what it was like to be in that band. The actors were incredible. Kristen Stewart [who plays Joan] was great. She’s a real person, down-to-earth, authentic. She put real pressure on herself to do the work. We spent a lot of time together over the two weeks before we started shooting. We were in the studio rehearshing, getting them to play instruments to the music. It was a lot for these girls to become a band in a short time, but by the time we started shooting they had a definite sense of ‘hey, we’re in a band’. It’s important that they were able to get that sense of camaraderie across.”
Source: Irish Times