"He continues to respond positively to treatment," said Graca Machel.
The 94-year-old is nevertheless said to remain in a critical state after five weeks in hospital.
On Thursday, President Jacob Zuma said the veteran of the struggle against white minority rule "remains as much of a fighter now as he was 50 years ago."
He was admitted on 8 June with a recurring lung infection.
Last week, President Zuma denied reports that Mr Mandela was in a vegetative state.
Several people who have seen him since say he was conscious and responsive.
The BBC's Karen Allen in Johannesburg says Mrs Machel has been a constant presence at Mr Mandela's side in hospital and has largely been kept away from the legal rifts within the Mandela family which have been exposed in public over the past few weeks.
She is the former president's third wife. They married on his 80th birthday.
Officials have urged South Africans to prepare to celebrate his 95th birthday next week.
Mr Mandela is revered across the world for his role in ending apartheid in South Africa.
He was jailed for 27 years, before being freed in 1990 and elected president in 1994.
He stepped down five years later.