Her article in thepeerage is here.
From antique-royals.tumblr.com/image/157679318658. I believe this image is cropped from an image posted by the UK National Portrait Gallery.
While the National Portrait Gallery dates this to 1906 (when she married), the leg-o-mutton sleeves and yoke bodice suggest the middle 1890s. Barnett started his practice in London in 1890 and she was born in 1878. The pleated modesty piece resembles that worn by Princess Victoria in 1905 and this dress has a basque waistline, perhaps from a Swiss belt. If this is a 1906 photo, she is dressing retro.
Keywords: Barnett, Ivy Muriel Dundas, Ivy Muriel Chamberlain, Dundas family, Chamberlain family, British, wave coiffure, earrings, under-bodice, sweetheart neckline, floral bodice ornament, elbow length leg-o-mutton sleeves, yoke over-bodice, Swiss belt, basque waistline, close skirt