 In January 2015, Williams (a victim of cyberbullying herself) starred as Casey Jacobs in the one-hour-long BAFTA nominated "Cyberbully", a Channel 4 docudrama television film.Writing for "The Guardian", Filipa Jodelka described Williams' central, almost solo, performance as a "tour-de-force".In Autumn 2015, Williams guest starred in four episodes of series 9 of the BBC science fiction series "Doctor Who" ("The Girl Who Died, The Woman Who Lived, Face the Raven" and "Hell Bent"), in the recurring role of Ashildr, a Viking girl made immortal by the Doctor.