The Victoria and Albert Museum has posted numerous Lafayette Photographic Studio portraits of late Victorian, Edwardian, and more recent aristocrats here. Following are most of their notes for these and other images of Baroness Agnes de Stoeckl:
“...Biog: m. (1892) Baron Alexander de Stoeckl, Russian diplomat and gentleman-in-waiting to Grand Duchess George (Princess Marie of Greece). In the mock obituary she added to the front of her autobiography, she wrote: 'She spent the greater part of her life amidst the courts of Europe, and she was called 'Aunty Ag' by half the royal personages.’
The Spectator, 12 JANUARY 1951, Page 22
Not All Vanity.
By Baroness de Stoeckl. (John Murray.. IRS.) In 1892 Agnes Barron, aged eighteen, married Sacha de Stoeckl. Attachd at the Russian Embassy in London, who later became Equerry to the Grand Duke Michael and finally Comptroller to the Grand Duchess George.
Her parents were Irish; her father's vast wealth was derived from Mexico, but he made his home in Paris and entertained the fashionable world on a princely scale. At the start of her diplomatic life in London, Baroness de Stoeckl found that it was necessary to do 'much hard work resting' to look fresh. She would begin the exhausting process of dressing at four o'clock, whether the party was a dinner at eight-thirty or a ball at eleven. Sleeves were so enormous at that time that her husband could not sit beside her in the brougham; he had to follow in a hansom.
The Grand Duke Michael, who lived permanently outside Russia. regarded himself, like the other Grand Dukes, as a being apart. Lunching once in public with the authoress (i.e. Baroness de Stoeckl), he insisted on sitting on a large soufflé, roaring with laughter as he did so. Agnes de Stoeckl visited Russia for the first time after her husband had joined the Grand Duchess George. She and her daughter, Zola, were made much of by Tzar Nicholas, who, in 1914, gave her land in the Crimea on which he intended to build her a house.
According to the museum’s notes, these photos date to 11 August 1902 while Edward VII was crowned on 9 August 1902.
I cannot find photos of Baroness de Stoeckl in other dresses.
The left image is from theimperialcourt.tumblr.com/page/2 and the right image is from pinterest.com/jmjm94/romanov/. This paired image is 44.38 cm high at 28.35 pixels/cm.