The businesswoman is the first daughter of Mandela’s marriage to his former wife Winnie.
“Her appointment represents a clear recognition of the importance the South African government attaches to the relationship with Argentina,” the Foreign Ministry of Argentina said in a statement.
“During the presidency of Nelson Mandela, recognised as a global figure for his fight against apartheid and for human rights, Zenani Dlamini accompanied her father to act as First Lady of her country,” it said.
Zenani Mandela-Dlamini was a child when Nelson Mandela was in prison. She married into the Swaziland royal family but later divorced her prince husband.
South African foreign ministry officials were not immediately available for comment.