Kelly joined the cast of "Liar" for its second series in 2020, playing Detective Karen Renton. A character bio for Renton describes her as an “unconventional” officer, whose “bluntness” often ruffles feathers. Of her role, Kelly stated “It's my belief that Karen Renton is that way because she has to be that, and if she wasn't that, I wouldn't believe that out of all the detectives that they could send from the Met to solve this front-page news story, why would they pick her if she wasn't excellent at her job?," she said. “I think she would have been chosen because she can act very quickly and very swiftly, and she has great instincts.