According to The Daily Mail, a source revealed the duchess felt "taken advantage of".
The insider - a close friend - made the shock claim, just months before the royal is expected to give birth.
The first announcement of the book - which is yet to be released - was made by Samantha in April 2016. She recently announced the works of a second book, titled In The Shadows of the Duchess.
It's been revealed that The Diary Of Princess Pushy's Sister is set to be published in April – to co-incide with the birth of Meghan and Prince Harry's first child.
According to Samantha, the expose will "cover everything from behind the scenes that the world does not know about," she told The Daily Star.
The Daily Mail source said that Meghan stopped looking at news articles about herself after learning about the book and advised close family and friends to do the same.
"She stopped reading things after finding out about her sister's book,' the friend said. "She cried when she found out about it."
She insider added, "Out of everything that's been said, the one thing that really upset her was that [the book]."
"She and Samantha never had a very good relationship and she feels her sister is using her position for profit."
Meghan is believed to have last seen her half sister in 2011 and has not been in touch with their father - Thomas Markle Snr since he missed her May 2018 nuptials.
Since then, Thomas has staged a series of publicity ploys to guilt Meghan to getting back in touch with him.
"It's not fair what he's done," the source told The Daily Mail. "He's always known how to get in touch with her and they've never been as close as he's made out"