It looks like 30 October was the day the Plunketts visited Camille Silvy's photo studio. According to her article in thepeerage, she married one Colonel John Douglas Johnstone and had three children.
From Paul Frecker; sepia tone removed (and re-added to borders with Photoshop) by gogm.
The vertical stripes, belt, and pelisse bodice make this photo a must for posting. She appears to be wearing long sausage curls that may be a reflection of her youth.
Keywords: 1860, Silvy, Plunkett family, Johnstone family, British, long straight coiffure, feathered hat, high neckline, collar, pelisse bodice, long sleeves, belt, natural waistline, crinoline, over-skirt, shawl, neck band, bracelets