Winnie Mandela raises her fist during the funeral for 17 people who were killed during fierce rioting on Wed. March 5, 1986 in Johannesburg's Alexandra township. AP hide caption toggle caption AP JOHANNESBURG, South Africa —Winnie Madikizela-Mandela is one of the most revered —and controversial — women in South African history, but to her grandchildren the anti-apartheid icon was always just their beloved 'Big Mommy.'  Now two of Mandela's granddaughters are reexamining her divisive legacy in a new Netflix documentary series called The Trials of Winnie Mandela , currently only available in Africa. In the trailer for the series, sisters Princess Swati Dlamini-Mandela and Princess Zaziwe Mandela-Manaway acknowledge they have set themselves a hard task, asking "How do you ask your grandmother, are you a murderer, are you a kidnapper?'"  But they think they managed to present an unbiased portrayal of Winnie in the series.…