Blamed for the killing of activist Stompie Seipei, who was found near her Soweto home with his throat cut, she was convicted in 1991 of kidnapping and assaulting the 14-year-old because he was suspected of being an informer.
Her six-year jail term was reduced on appeal to a fine.
She and Mandela separated in 1992 and her reputation slipped further when he fired her from his cabinet in 1995 after allegations of corruption. The couple divorced a year later, after which she adopted the surname Madikizela-Mandela.
Appearing at the Truth and Reconciliation Commission (TRC), set up to unearth atrocities committed by both sides in the anti-apartheid struggle, Madikizela-Mandela refused to show remorse for abductions and murders carried out in her name.
Only after pleading from Archbishop Desmond Tutu, the anguished TRC chairman, did she admit grudgingly that "things went horribly wrong."
Four years later, she was back in court, facing fraud and theft charges in relation to an elaborate bank loan scheme.
Strikingly attractive and with a steely air — her given name, Nomzamo, means "one who strives" — the 22-year-old Winnie caught the eye of Mandela at a Soweto bus-stop in 1957, starting a whirlwind romance that led to their marriage a year later.
But with husband and wife pouring their energies into the fight against apartheid, the relationship struggled before being torn apart after six years when Mandela was arrested and sentenced to life in prison.
Madikizela-Mandela later described her marriage as a sham and the birth of their two daughters, Zindzi and Zenani, as "quite coincidental" to her one true love — the struggle against white rule.
"I was married to the ANC. It was the best marriage I ever had," she often said.
Graca Machel, who became South Africa's first lady when she married Nelson Mandela in 1998, paid tribute to her predecessor in the years afterward.
Nelson Mandela died in 2013 and made no mention of Madikizela-Mandela in his will.
Madikizela-Mandela revealed her contempt in 2010 for the deal her ex-husband struck with South Africa's white minority nearly two decades before.
In a London newspaper interview, she attacked Mandela, saying he had gone soft in prison and sold out the black cause.
"Mandela did go to prison and he went in there as a burning young revolutionary. But look what came out," she said. "Mandela let us down. He agreed to a bad deal for the blacks."
She also dismissed Tutu, post-apartheid South Africa's moral fulcrum, as a "cretin" and criticized his attempts at national healing as a "religious circus."
"I am not sorry. I will never be sorry," she said. "I would do everything I did again if I had to. Everything."