In a Tuesday Instagram post, Suzannah, who designed Sophie's dress, called it "an absolute honour and privilege to be given this opportunity to be a small part of modern history yesterday."
After thanking Jenny King Embroidery for "enabl(ing) the making of this beautiful coat dress design for HRH Countess of Wessex," the designer shared that the design was a tribute to the Queen's "favorite flowers."
"Many beautiful panels of Italian wool and silk satin were embroidered as a tribute with Lily of the Valley — Her Majesty's favourite flowers, intertwined with florals from her wedding bouquet," Suzannah added.
At Monday's funeral, Sophie also carried the Launer "High Society" clutch in ebony black.
After, another guest exclusively told PEOPLE that the royal had remarkable resolve at the emotional service for her mother-in-law and has been a rock for her relatives as they mourn the Queen.
"The Countess of Wessex was incredible. I saw her putting her arm around three or four people," lawyer Pranav Bhanot told PEOPLE on Monday. "It felt like she was really the glue keeping everyone quite strong today."
Kirsty O'Connor - WPA Pool/Getty Sophie, Countess of Wessex
"She really seemed to be the person keeping the family together," Bhanot explained. "There were a few bishops who started crying when they saw the Queen and she was kind of comforting them, even though she is the direct family member."
The guest, 34, said that Sophie was warmly there for everyone around her, including Kate Middleton.
"She put her arm around Kate's shoulders towards the end too. It was comforting," Bhanot said, reflecting on what the move meant.
"From where I was I got the sense that ... sometimes you have that one strong person in a family who's kind of keeping everyone together. To me, it seemed like Sophie was that person today," he added. "It was something that really stood out because it seemed that she really was very strong."