The sitter in this portrait is Emily Scoble, a model from the Slade School of Art. Orpen was briefly engaged to her. The room is apparently an accurate portrayal of Orpen’s lodgings, but the shallow pictorial depth and decorative, or ‘aesthetic,’ arrangement of objects is based on Whistler’s famous portrait of his mother in profile. The circular mirror on the wall reflects the artist painting at his easel. This is a device which Orpen borrowed from a 15th-century painting by Jan van Eyck, The Arnolfini Portrait, which he would have seen on display at the National Gallery.
[http://www.tate.org.uk/art/artworks/orpen-the-mirror-n02940]
By the 1900s, William Orpen stands out as the figure most consistently toying with the van Eyckian mirror for the purposes of displaying his own artistic identity. Orpen owned a convex mirror, which is on display in the exhibition, and employed van Eyck’s display of his self (assuming we accept that hypothesis) in The Mirror (1900, Tate) in which we can see a reflection of a brass chandelier and Orpen can be seen painting.
[https://madeleineemeraldthiele.wordpress.com/2017/10/24/reflections-van-eyck-and-the-pre-raphaelites/]