Kristen Stewart's most challenging role to prepare for was her portrayal of Jean Seberg in the 2019 biopic Seberg. To get into character, Stewart tried to emulate Seberg's distinctive voice and mannerisms, and she also researched the actress's life and career to better understand her motivations and personality.
Stewart has said in interviews that she was drawn to the role because of the complexity and depth of Seberg's character, and she wanted to do justice to her story. She also revealed that she spent hours watching Seberg's interviews and films to get a sense of her personality and to capture her essence on screen.
In addition, Stewart has mentioned that she worked closely with the film's director, Benedict Andrews, to ensure that her portrayal of Seberg was accurate and authentic. She also consulted with Seberg's friends and colleagues to gain a better understanding of her personality and character.
Overall, Stewart's preparation for the role of Jean Seberg was extensive and meticulous, and her dedication to the role earned her critical acclaim and a nomination for an Academy Award for Best Actress.