The film has remained in limbo for almost 2 years. Production lasted from May to June 2016, and the film wasn't theatrically released until March 9th, 2018. This was due to a long and extensive festival circuit in 2017, not to mention post-production and marketing.
The trivia item below may give away important plot points.
The 'killing' scene is done as it would have been on stage, according to director Cory Finley, with the camera staying in the living room on Amanda (Olivia Cooke) while Lily (Anya Taylor-Joy) goes upstairs, and off frame, to do the deed. In reality, Taylor-Joy was being prepped with fake blood in real-time, ready for her return to the scene near its end.