In Grant's latest Twitter rant Friday, she wished Markle a happy birthday by complaining about the late birthday card Kensington Palace sent their father, Thomas Markle.
"Happy Birthday Meg! It would be so lovely and appropriate of you to send DAD a BELATED birthday card for his July 18th [cake emoji] [Kensington Royal] Cheers," Grant wrote on her private Twitter account, The Daily Mail reports.
Grant also shared a link to an Elle article on reports of Markle and Prince Harry "retreating" from the spotlight because of her family's constant critical comments.
"OK so Cruella Deville is retreating [laughing out loud] let me know how that works out for you," Grant wrote, reports The Evening Standard.
"There are smoke and mirrors you try to hid things with, but you can't hide from what you see in the mirror," Grant continued.
In a series of tweets last month, Grant slammed Markle for not speaking with their father.
"How about you pay tribute to your own father?! Enough is enough," Grant wrote. "Act like a humanitarian act like a woman! If our father dies I'm holding you responsible, Meg! [Kensington Royal]."
When Grant made an appearance on Good Morning Britain, she pleaded with Markle to speak with their father again.
"He's very worried about her given the distance and the inability to have live communication, so he just needs to know that she's well, she's happy, she's OK and to touch bases, so I hope they get to do that soon," Grant said.
Thomas Markle, 74, has said he has not spoken with Markle since she married Prince Harry on May 19. Thomas was invited to the wedding, but missed out after suffering a heart attack just days before it. Harry's father, Prince Charles, walked Markle down the aisle.
Markle's fans were not pleased with the Cruella de Vil comparison, with some even suggesting Grant fits the bill better than the former Suits star.
"YOU are seriously calling The Duchess Cruella De Vil? That’s pretty rich coming from you. What a bitter hag. Loooool," one person wrote, adding a photo of Grant and the 101 Dalmatians character side-by-side.
"You're absolute trash! She's right to cut you out of her life & your loser dad, too," another Markle fan wrote.
@SammyMarkle64, you're absolute trash! She's right to cut you out of her life & your loser dad, too!— 🌊(((Pat Rice)))🌊 (@PatRice85552156) August 4, 2018
Samantha Grant Trolls Meghan Markle on Her Birthday, Calls Her Cruella De Ville https://t.co/XQIVlLHIFj via @Yahoo
"These are some ignorant nonsensical people. You want to get in touch with someone because you are worried about them and want to know how they are so you take to MSM and mock and insult them?" one Twitter user wrote.
These are some ignorant nonsensical people. You want to get in touch with someone because you are worried about them and want to know how they are so you take to MSM and mock and insult them? #brainDamagedMarkles #SamanthaMarkle #ThomasMarkle https://t.co/dz0sLxq1Kl— Anyim Moore (@animosity_foru) August 4, 2018
One Twitter user called Grant a "mentally unbalanced moron."
Earlier she called her "cruella deville" and was hoping for a divorce between Harry and Meg. Now she is wishing her happy birthday. Mentally unbalanced moron 😂🤣. Why "willful" Meg should send a birthday card to her abusive father?— Raphaëlle-Esther J. (@RaphaelleEsther) August 4, 2018
"Cruella de Vil? Oh I don't think you're quite that bad. Then again maybe you are. If the shoe fits," another wrote.
Cruella de Vil? Oh I don't think you're quite that bad. Then again maybe you are. If the shoe fits...— MWP (@hiatlas) August 4, 2018
Photo credit: Mark Cuthbert/UK Press via Getty Images