She said she had 'toiled over every detail which could be manipulated'.
Jason Knauf, who was communications secretary to Meghan and her husband Prince Harry until March 2019, said in a statement to the Court of Appeal in London the duchess had told him that she had known it was possible that her father would release the letter.
He said Knauf's evidence cast doubt on the original ruling, adding that the case should have gone to a full trial.
Associated Newspapers Limited on Tuesday began an appeal against a ruling that its publication of parts of the letter to Thomas Markle breached her privacy.
It has not yet done so because of the appeal, in which lawyers for the publishers argue that the letter was written with the knowledge that it could be made public.