She was 42.
The family of Marcy Borders first announced her death Monday on Facebook.
Borders, who was 28 at the time of the attacks, was just one month into a job for Bank of America in one of the Twin Towers.
As one of the towers collapsed, she took refuge in a nearby office building, where AFP photographer Stan Honda took a haunting photo of her completely covered in a thick layer of ash, which earned her the moniker of "The Dust Lady."
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"I can't believe my sister is gone," her brother Michael Borders wrote on Facebook, asking for people's prayers.
Her cousin Elnardo Borders wrote: "May God Comfort .Us in our time of sorrow. My emotions are all over the place right now."
He later wrote: "She @ peace now!!!"
After the attacks, Borders spiraled into a decade-long deep depression and alcohol and drug abuse, though she eventually recovered after several years.
She lost her job at Bank of America, where she ignored repeated offers of a transfer.