The Irish star researched her character for the film, which tackles the prickly relationship between Mary Stuart and her cousin, the formidable Queen Elizabeth I - and she's convinced history would be different if it wasn't for the liars who wanted to bring the Scottish ruler to her knees.
Although the action is set more than 500 years ago, the Oscar-nominated star is adamant what happened then isn't so dissimilar to problems facing the modern world.
"I think it's just that whole issue that we're dealing with now with 'fake news' and stories being warped in order to suit one political side or the other," she tells Vulture. "That's exactly what happens in Mary's case."
"The Casket letters that eventually lead to Mary's death were essentially copied and edited by William Cecil, whom Guy Pearce plays. He just had it out for Mary from the very beginning and really hated her, and would stop at nothing to destroy her. And he actually did."
"He took private letters that she had sent to a personal friend of hers and confidantes, and he changed them. He actually edited the letters and made it seem as though she was plotting to kill Elizabeth while she was under house arrest. That's the kind of barbarity that we're experiencing right now, especially in the U.S."