In 1907, the Baroness de Meyer was painted  in Venice by Sargent's friend William Bruce Ranken (1881-1941). It very well could have been in Venice where Sargent sketched her.

From: Europeanpaintings.com 

8/15/02

Maria Beatrice Olga Alberta Caracciolo (born in London 8 August 1871) was the daughter of the Duchess of Castelluccio, and rumored to be the natural daughter of Albert Edward, the Prince of Wales and later King Edward VII, a onetime lover of the Duchess (Olga's mother).

Olga, given the name Alberta in honor of the Prince who was also her godfather, was the only daughter and heiress to her father’s title of Duke of Castelluccio. Circumstantial evidence and the many favors later shown her and her second husband, the brilliant society photographer Baron Adolphe de Meyer, by the King (whose goddaughter she was), were thought by some to support the rumors regarding her paternity, which were never disproved.

Olga first married at Naples 11 May 1892 an Italian nobleman, Nobile Marino Brancaccio, younger son of Carlo Brancaccio, Prince of Triggiano and Duke of Lustra, but this marriage ended in divorce (7 June 1899) and she remarried to Adolphe de Meyer. Her beauty and elegance inspired not only Blanche, but also Whistler, Boldini, Sickert, Sargent, Conder, and Helleu to paint or draw her. The [French painter Jacques-Emile Blanche], reminiscing about Olga in his memoirs, wrote: she "has such a wealth of dresses, fans, and jewelry as befitted one who put in an appearance at all important social functions. When Olga enters the Orchestra stalls, the opera glasses of everyone were focused on her, the most elegant woman in the audience, the most thoroughbred of cosmopolitan society: ‘Here is the Baroness de Meyer,’ they whisper spellbound." 

Her husband was an art collector of some note, one of the first owners of a Monet series painting (the Houses of Parliament) as well as other impressionist works. 

(Europeanpaintings.com)