Samantha, 57, is suing the Duchess of Sussex, 41, over claims made in her Oprah Winfrey interview and the Finding Freedom unauthorised biography. A Florida judge has set an October 2023 trial date for the defamation case if they fail to settle or resolve it in mediation.
Samantha, who is is seeking $75,000 (£57,000) in damages, contests Meghan saying in her TV interview that she “grew up as an only child”.
She also claims Meghan told “false and malicious lies” about her fairytale “rags-to-royalty” upbringing at her paternal family’s expense.
And Samantha claims the Finding Freedom book subjected her to “humiliation, shame and hatred on a worldwide scale”.
It comes after Meghan’s legal team moved to dismiss the case in papers submitted to the Florida court in July.
If they fail to settle or resolve in mediation, a trial date has been set for October 2 2023 which would last no longer than five days.
In a previous statement, Meghan’s lawyer Michael Kump hit out at Samantha’s legal action.
He said: “This baseless and absurd lawsuit is just a continuation of a pattern of disturbing behavior.
“We will give it the minimum attention necessary, which is all it deserves.”
Samantha has been a vocal critic of her half-sister in a series of media appearances as the pair have clashed over versions of their childhoods.
She also released her memoir The Diary of Princess Pushy’s Sister last year.
Meghan is estranged from much of her paternal family including her father Thomas Markle and her half brother Thomas Markle Jr.