The ruling also let Meghan off the hook for misleading the court in denying that she engaged with the authors of a flattering book about the couple.
The statement, the court said, had no bearing on the legal question of whether The Mail violated her privacy.
Lawyers for The Mail’s publisher, Associated Newspapers, argued that Meghan’s involvement in trying to shape the book showed a pattern of careful management of her public image.
The Mail cited emails between the duchess and her communications secretary at the time, Jason Knauf, in which she asked him to review a draft of the letter.
The court acknowledged that the new evidence suggested Meghan worried the letter might be leaked.
For Harry and Meghan, who have been in a feud with the tabloids, it was a striking victory but not one that seemed likely to end the bitterness between them and the news media.
“In the nearly three years since this began, I have been patient in the face of deception, intimidation and calculated attacks,” the duchess said in a statement.
Meghan, who now lives with Harry and their two children in Montecito, Calif., has recast herself in the United States as a celebrity, a business owner, an investor and a social activist.