From: Tate Gallery

Hylda was the third daughter of the wealthy art dealer Asher Wertheimer . . . The portrait of Hylda is in the grand manner of the old masters, and great care is given to the depiction of the different luxurious textures of her clothing. Sargent tried to dissuade Hylda from wearing her pince-nez, which undermine this illusion, but they were retained at her insistence. 

(From the display caption June 2002 Tate Gallery)