Makaziwe Mandela told South Africa's state broadcaster on Thursday that the former president and anti-apartheid leader is still giving the family hope, even though "anything is imminent."
She says her family will wait with 94-year-old Mandela until "the time to go." Makaziwe Mandela's comments were posted on the SABC web site.
Mandela, South Africa's first black president, is revered among most of the country's 53 million people as the architect of the 1994 transition to multi-racial democracy after three centuries of white domination.
However, his latest hospitalization - his fourth in six months - has reinforced a realisation that the father of the post-apartheid "Rainbow Nation" will not be around for ever.
The deterioration in his health at the weekend to "critical" from "serious but stable" caused a perceptible switch in the national mood, from prayers for his recovery to preparations for a fond farewell.
Maharaj added that it was too early to say whether the seriousness of Mandela's condition could force changes to the schedule of a planned visit to South Africa this weekend by U.S. President Barack Obama.
Obama is also visiting two other African countries, Senegal and Tanzania, starting in the Senegalese capital on Wednesday night.
Well-wishers' messages, bouquets and stuffed animals have piled up outside Mandela's Johannesburg home and the wall of the hospital compound where he is being treated in the heart of the capital.
"We know that the day will come when he passes but it is so painful to accept," said Patricia Ndiniza, 53, an estate agent who left a note wishing Mandela a speedy recovery.
"He is a pillar for all of us. He is our pillar of peace and reconciliation," she said.