Angela Kelly said she wears the queen's shoes before appointments to make sure they are comfortable.
The monarch and her seamstress share the same shoe size and, as the queen has little time for herself, Kelly wears the shoes for her.
The revelation is contained in Kelly's new book, The Other Side of the Coin: The Queen, the Dresser, and the Wardrobe.
As for shoes, she said, "It makes more sense like that.
"As reported in the press, a footman wears Her Majesty's shoes to ensure they are comfortable and ready to go.
"And yes, I'm so crazy."
Kelly also wrote about the meeting between First Lady Michelle Obama and the Queen, when Obama broke protocol and touched the Queen's back.
"The queen has the ability to make everyone feel so relaxed that sometimes it seems instinctive to be tactile to her, just as Michelle Obama demonstrated during the State Visit with her husband, President Obama, in 2009.
"Much has been done about the meeting between Michelle and Her Majesty, when an instant and mutual warmth was shared between these two remarkable women, and the protocol was abandoned as they were standing, hugging each other behind their backs."
She had a cameo appearance on a 2012 James Bond sketch
Kelly also writes about the queen's part in a James Bond sketch at the 2012 London Olympics opening ceremony, suggested by film director Danny Boyle through the queen's private secretary, Edward Young.
"There are few occasions when His Majesty will agree to break the protocol, but in 2011, when film director Danny Boyle approached the Royal House, he had a request to do so that we simply could not refuse," she said.
"She was very amused by the idea and immediately agreed. I asked if she would like to speak. Without hesitation, Her Majesty replied," Of course I must say something. After all, he is coming to rescue me. " .
Kelly said she asked the queen if she would like to say, "Good evening, James," or "Good evening, Mr. Bond," with the monarch choosing the latter.
She said, "In a matter of minutes, I was back in Edward's office delivering the good news to Danny – I think he almost fell out of his chair when I said the queen's only stipulation was that she could deliver that iconic phrase: & # 39; Good night, sir.