"The defence lawyers will probably argue any communication she had with friends over the People article is relevant," a source told The Sun.
"But if her lawyers were sensible they would have looked through all her communications before making the claim to know what could possibly end up being revealed."
The Duchess is set to give evidence at the trial and be cross-examined by lawyers from Mail on Sunday publishers Associated Newspapers.
"The Duchess of Sussex is very clear as to what the litigation against Associated Newspapers involves and is resolute in her determination to see the case through, in order to hold the tabloid to account for its actions," her spokeswoman told The Sun.
"The lawyers will want Meghan in the witness box and she will be open to a cross-examination, which could see many aspects of her family background examined in court.
"That's the downside of suing in the public domain. She will be under oath so the stakes are very high for her.
After Markle's husband Prince Harry accused the press of waging a "ruthless campaign" against his wife - Associated Newspapers said they stood by the story they published and will be "defending this case vigorously".