In 2017, Williams starred, alongside Bill Milner, as Lucy in the Netflix science-fiction teen superhero thriller film "iBoy". Tristram Fane Saunders of the "Daily Telegraph" felt she brought "depth, humour and honesty to the role." Also in 2017, Williams appeared as Isabel Baxter in "Mary Shelley" a romantic period-drama film directed by Haifaa al-Mansour and written by Emma Jensen. In 2018, she voiced the character "Goona", a Bronze Age fearless rebel tomboy football enthusiast in Nick Park's animated prehistoric comedy sports film "Early Man" that also featured Eddie Redmayne and Tom Hiddleston, though both Gwilym Mumford of "The Guardian" and Kate Stables of the British Film Institute noted that her accent varied during the film. From 18 October to 24 November 2018, Williams starred as Caroline in the stage play "I and You", which was written by Lauren Gunderson. The play premiered at the Hampstead Theatre in London. The play did well at the box office and Willliams' stage performance was regarded a critical success, with the production later being broadcast free on Instagram from 30 November to 3 December 2018 and again during the last week of March 2020. She also starred in the eleven-minute short film "Corvidae", a dark fairy tale filmed in 2013 and released in 2018, of which Craig Holton of "flickfeast" commented that Williams brought "an undeniably ethereal quality to this short film, helping it make the leap from grounded realism to eldritch bucolic fantasy".