Militant groups from Al-Qaeda and its offshoots to the Islamic State (IS) have sought the 42-year-old's release in exchange for captives, most recently the US journalist James Foley, beheaded by IS in August.
In an interview with AFP in the sprawling, violent Pakistani port metropolis of Karachi, Siddiqui's family protested her innocence and despaired at the horrors associated with her name.
Siddiqui's story, one of the most intriguing of the "war on terror" era, began in March 2003 when Al-Qaeda number three and alleged main 9/11 architect Khalid Sheikh Mohammed was arrested in Karachi.
Soon after his arrest, Siddiqui -- suspected of Al-Qaeda links by the US -- disappeared along with her three children in Karachi.
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The few US media reports about the incident described her as the first woman to be suspected of links to Osama bin Laden's terror network -- earning her the moniker "Lady Al-Qaeda".
Five years later she turned up in Pakistan's wartorn neighbour Afghanistan, where she was arrested by local forces in the restive southeastern province of Ghazni.
The Afghans handed her to US forces who began questioning her. During her interrogation she grabbed a rifle and opened fire, according to witnesses, at US agents while screaming "Death to America" and "I want to kill Americans". The soldiers escaped unhurt, but she was injured.
From Afghanistan, Siddiqui was put on trial in the US and sentenced in 2010 to 86 years for attempted murder -- and not for any Al-Qaeda links.
Even the US trial judge Richard Berman acknowledged in his verdict that it had "never definitely been established why Dr Siddiqui and her son were in Afghanistan".
Her supporters claim she was the victim of a secret Pakistan-US plot.
According to her family, Siddiqui and her three children -- Ahmed, Mariam and little Suleiman, then six months old and today dead -- were about to leave their house in the posh Gulshan-e-Iqbal district of Karachi for the airport when they were apprehended by Pakistani and US agents.