Lee Hee-ho, whose husband Kim Dae-jung tried to improve relations with the North, is the highest-profile of two delegations allowed by the South.
Officials said Mrs Lee, 89, was not representing the government. She will not stay for the funeral on Wednesday.
Meanwhile, state media in the North continues to promote Kim Jong-il’s son, Kim Jong-un, as his father’s successor.
The Rodong Sinmun newspaper has described Kim Jong-un as the head of the Workers’ Party Central Committee, meaning that he now controls one of the country’s highest decision-making bodies.
The newspaper earlier gave him the title of “supreme commander” of the armed forces.
Seoul has allowed only two private delegations to travel north to pay their respects, and will not be sending any officials to the funeral.
Mrs Lee, who met Kim Jong-il during a landmark summit in 2000, said in a statement that she hoped her visit would help to improve relations on the peninsula.