Meghan Markle's half-sister has questioned the future Royal's motives for the humanitarian work she has dedicated much of her time to.
Her charity projects have included trips to Rwanda to support a clean water campaign and to India to get better education conditions for girls in her drive for gender equality.
Samantha Markle said: "I've seen in my lifetime a lot of situations where celebrities visit a place which is poverty stricken and they're wearing impeccable clothing, they themselves are wealthy.
"And it really feels like just a photo opportunity, so that is a little exploitative in my mind."
The writer has also told Prince Harry's fiancee to "step up to the plate" and help their bankrupt father rebuild his life.
Samantha criticised her for not making the welfare of Thomas Markle "a priority", with the award-winning lighting director having lived a reclusive life in Mexico since being declared bust in 2016.
Samantha, one of two children Mr Markle had before he met Meghan's mother Doria, said the future Royal "owes" her father for helping her launch her successful acting career.
Speaking to Australian outlet Nine News from her Florida home, the 53-year-old said: "I think he did help her a lot and he is very creative too and encouraging, so she made the most of her environment.
"I don't think he feels that she owes him, but that is how I see it."
And in an apparent reference to Meghan's attire in the Royal couple's official engagement photos, she added: "If you can afford $75,000 (£53,535) for a dress, you can afford $75,000 to help your dad. That's how I feel, what's who I am.
"Honestly – what she could spend in a weekend would greatly help dad, so that should be a priority. I think you need to step up to the plate and make sure he is well taken care of."
Samantha claims to have asked the former Suits star for financial help for their father, but has so far not received any.
Samantha, who suffers from multiple sclerosis and is wheelchair-bound, says she has not spoken to Meghan, 36, for three years, despite Meghan promising to "keep in touch" after their last catch-up.
She says she has also distanced herself from half-brother Thomas Jnr, who was arrested last year for allegedly holding a gun to his girlfriend's head during a row.
More from Meghan Markle
But despite her comments, she insisted she was not "bitter" about the life her half-sister has enjoyed.
And in an interview with the Mirror last month, Samantha said she still hoped to be invited to the Royal wedding – and apologised to Meghan for previously going public with negative comments about her.