"He's doing well," she said after giving a speech on neonatal care just outside Johannesburg. "That's why I am here."
The 94-year-old anti-apartheid icon was released from hospital on April 6, after a 10-day stay during which he was treated for pneumonia.
His release was decided "following a sustained and gradual improvement in his general condition," the South African government said at the time.
He is currently receiving "high care" at his Johannesburg home, after the latest in a series of health scares.
Mandela was rushed to hospital before midnight on March 27, suffering from a recurrence of a lung infection.
Doctors drained a build-up of fluid, known as a pleural effusion or "water on the lungs", that had developed.
His hospitalisation left many worried about the increasingly frail health of a man who is seen as the father of modern South Africa.
It was the third time in five months that the former president has been hospitalised.
In March he was admitted for a scheduled check-up and in December he was hospitalised for 18 days for a lung infection and for gallstones surgery.
That stint was his longest since he walked free from 27 years in jail in 1990.
While Mandela's health is a topic of national conversation, many South Africans have come to accept their ageing icon's mortality.
Nearly twenty years after he came to power he remains the unifying symbol in a country that is still riven by racial tensions and deep inequality.
As a symbol Mandela bestrides South African politics, even if the man has long since left the political stage and for many of the country's large young population he is a figure from another era.
Machel's return to public engagements signals Mandela may be in a better state than many feared.
After delivering a speech on saving newborn babies, Machel said she would not be making public addresses if Mandela were not doing okay.
"I wouldn't if he wasn't," she said.
Machel was speaking at the opening of a conference on neonatal care, where she said a lack of political will was holding back progress toward reducing newborn mortality rates.
Machel is a public figure in her own right.
She makes frequent speeches on health and has worked with the United Nations children's fund UNICEF.
She is Mandela's third wife and is the widow of Mozambique's former leftist president Samora Machel.
During the Cold War, his Russian Tupolev airplane crashed into mountains just a few kilometres from the border between Mozambique, South Africa and Swaziland on the night of October 19 1986.
An inquiry led by South Africa's fervently anti-communist government blamed the Russian crew for the accident which killed 35 of the 44 aboard, including government ministers and academics.