She helped to organise a publicity day in London on June 30 for Suits, the US drama in which Markle starred.
Markle thanked von Westenholz on Instagram, announcing that she was wearing Ralph Lauren head-to-toe.
Von Westenholz was a regular on the royal family's annual skiing trip to Klosters. In 2000, when aged 16 she and her sister Victoria, 13, accompanied princes William and Harry on their annual week-long skiing trip.
Press reports described the von Westenholz girls as part of a 15-strong royal party.
The sisters are an integral part of the prince's circle of close friends and trusted confidantes. Von Westenholz has been photographed at parties with the likes of Guy Pelly, who at one time was ever present on the princes' social circuit.
Von Westenholz' sister had previously been touted as a possible future bride for Prince Harry before dashing all those hopes by marrying a different Old Etonian in 2014.
Their parents Baron Piers von Westenholz and his wife, Jane, are close friends of Prince Charles. The baron, 73, an antiques dealer and interior designer, is a former Olympic skier, competing for Britain at the Winter Games in Innsbruck in 1964.
Baron von Westenholz was entrusted with the $490,000 makeover of the Castle of Mey in Caithness, the former home of the Queen Mother, which is now run by a trust presided over by Prince Charles.
Von Westenholz declined to take sole credit for her matchmaking when approached, insisting others were involved.
"I might leave that for other people to say [who it is]," she said.
"It's a great story and I am sure they are going to be very happy together. I am just happy they are really happy. They are great together."
The royal matchmaker in chief appears to be single.
She has been linked, briefly, with pop singer James Blunt. Within the fashion industry, she has helped to push the Ralph Lauren brand.
But with her fixing skills, she has brought together from different worlds two people and made not only them happy, but put a smile on the nation's collective face.
