I cannot find information about C. Merlin or C. Mertin, photographer.
From queenvictoriasfamily.tumblr.com; spots removed with Photoshop and image enlarged one quarter and contrast increased.
Sophie wears clamshell-like epaulettes covering her sleeves, much like Alexandra of Edinburgh's, in this photo.
Keywords: Queen Sophie of Greece, Princess, Queen, Hohenzollern family, Glucksberg family, curly coiffure, scoop neckline, epaulettes, elbow length leg-o-mutton sleeves, vee waistline, close skirt, train, necklace, bracelets, fan