Per Charlie Brooker’s recollection of her involvement with the show, she played a significant role in fleshing out the narrative, and putting a personal stamp on the project.
She wasn’t just there to pick up a paycheck; she specifically wanted to add characteristics and trademarks that felt unique to her sensibilities as a filmmaker to give the episode a proper beginning, middle, and ending.
While quite a bit of Jodie Foster’s episode of Black Mirror (titled “Arkangel”) was already on the page when the story got to her, she was apparently incredibly willing to sit down and dive into the material.