Meriam Yahya has been condemned to death by hanging in Sudan, convicted of renouncing Islam and marrying her Christian husband.
Her brother Al Samani Al Hadi told CNN he turned his sister into authorities because his family are "Muslim people."
"It's one of two; if she repents and returns to our Islamic faith and to the embrace of our family then we are her family and she is ours," he said.
"But if she refuses she should be executed," he told CNN.
The sentence has prompted international outrage with Australian Foreign Minister Julie Bishop calling for Sudanese authorities to uphold religious freedom laws.
Meriam, who gave birth to a baby girl in prison last month, denies the charges against her and said she was raised a Christian.