In Interview with Screenrant :-
People were very skeptical when Kristen Stewart was initially cast in this film. But now seeing the trailer and all the footage, you really get why she’s perfect casting.
Rupert Sanders: “Yeah, I think we were looking for someone who was obviously a great actor first and foremost but also someone who’s incredibly physical. Everyone thinks she is Bella from Twilight. I think she’s such a good actor that she encompassed that role so well that people think that’s how she is. When you meet Kristen, she’s so far away from that character. I’d first seen her in ‘Into the Wild’ and I was really blown away. I remembered that she was the girl from ‘Panic Room,’ ‘Welcome to the Rileys,’ ‘The Runaways,’ and now ‘On the Road.’ She’s one those actors who does these smaller films and then she does these big movies and she’s really managed her career so well in that way. She’s incredibly spirited and very kind of wild and also she’s got this kind of this alchemy to her. You’re not quite sure what it is about her but on screen she’s just incredible. And when you see her act you realize why she is such a huge movie star and why she’s going to continue to get bigger.”