The 59-year-old former royal said she had to change seven times between Christmas Eve and Christmas Day to be dressed appropriately.
“There are mainly useful things, such as homemade jams, china or curios bought from county fairs. Then it will be lethal martinis and a black-tie dinner.
“There’s a really careful old-fashioned placement. It’s always boy-girl, boy-girl.”
Fergie's words will surely resonate with Meghan's mother, who is set to spend Christmas at Sandringham for the first time.
Jean Broke-Smith, royal expert, claims the rules and etiquette could turn the festive days into a challenge for Ms Ragland.
“There will be advisors on hand to help Meghan’s mum Doria Ragland, but it is going to be difficult," she told New Idea.
“For one thing she will need to bring a trunk full of clothes from California.”
They said: “It’s a mark of the Queen’s respect for Meghan and an acknowledgement that she doesn’t have any other relations in this country – unlike Kate who has the support of a very close family.”