The niece of Joe Lynskey, whose abduction and murder is also portrayed in the show, said that Mr Keefe did speak to them about the show, but that production had already begun.
“It had started, and there was no stopping it,” Maria Lynskey told BBC’s Evening Extra programme.
She added: “We told him how we felt about it, and that we didn’t approve of it.”
Joe Lynskey was a Cistercian monk who later became a member of the provisional IRA.
He disappeared in 1972 and Ms Lynskey told BBC News NI that the family initially believed he had fled to America.
But it was revealed in alleged admissions by former members of the IRA that he had been abducted and killed.
Despite a number of searches, Mr Lynskey’s body has still not been found.
Ms Lynskey said that she accepts the story had to be told “because it’s history” but said it was easy for people who weren’t involved to watch a drama based on these events.
“I would agree that any publicity is good, and if it helped young ones to stay away from [violence], then absolutely.”
But she added: “I don’t think I could watch it.”
“I know these families, I know what they’ve been through. To watch your mother being taken from her home when you were a child, or to see your brother in a bog with a gun to the back of his head, that becomes reality to you, you’re seeing it again.”