Graca Machel says the love and generosity from across the world has brought comfort and hope to her husband and their family.
"The messages have come by letter, by SMS, by phone, by Twitter, by Facebook, by email, cards, flowers and the human voice, in particular the voices of children in schools or singing outside our home," Machel said in a statement. "We have felt the closeness of the world and the deepest meaning of strength and peace."
The 94-year-old former South African president is in serious condition with a recurring lung infection.
President Jacob Zuma said Sunday that Mandela remains in serious condition but that his doctors are seeing sustained improvements. Zuma also said that Mandela is engaging with family during visits.
Machel and Mandela married in 1998, marking Mandela's third marriage and her second. Machel already has experienced the loss of a husband. Mozambican President Samora Machel, her first husband, died in a plane crash in 1986.
The Associated Press contributed to this report.