Cherie Curie apparently burst into Tears of Joy when she heard Dakota Fanning had been cast to play her.
Although Lita Ford did not allow filmmakers to adapt her life, she gave Scout Taylor Compton her approval.
Joan Jett likewise gave Kristen Stewart her approval, claiming the performance made her proud. She was even briefly fooled by a recording of Kristen playing one of her songs, assuming she was listening to one of her old demo tapes.
Cast the Expert: Subverted. Scout Taylor Compton already knows how to play the drums, so she auditioned for Sandy West for this reason. She however got the role of Lita Ford, and had to learn to play the guitar.
Dawson Casting: Averted. 15 year old Cherie was played by the then 16 year old Dakota Fanning, and Downplayed with Joan Jett, who was 17, played by the 19/20 year old Kristen Stewart. Additionally the movie takes place over a two year timespan, matching Stewart's age with Joan's by the end.
Dyeing for Your Art: Dakota Fanning cut her hair onscreen. Kristen Stewart also dyed and cut her hair into Joan's signature stylenote The Twilight Saga: Eclipse started production around the same time as The Runaways so she wore a wig for the former film - as well as learning how to play guitar. Scout Taylor Compton also got personal coaching from Lita Ford.
Real Life Writes the Plot: Lita Ford declined the rights to adapt her life for the film, though she did give Scout Taylor Compton some personal coaching - thus Lita's role in the film is small. Jackie Fox also refused to let the filmmakers use her, hence the creation of a Composite Character called Robin.