It is based on the play Blackbird by David Harrower.
The nipple ring on display in the shower scene is apparently Rooney Mara's own, having had it done for the film ' The Girl With the Dragon Tattoo'
Filmed in new Romney, Northampton, greatstone and Littlestone in Kent.
Although from distinctly different sources, this movie is extremely similar to "The Girl in the Book," which came out the previous year.
Una is an old Irish name for a female. It possibly derives from the Irish uan (lamb). It is generally considered to mean "the personification of truth, beauty, and unity." Oona is a more common alternative spelling of the word.