The flames broke out shortly after 1 a.m. on East 49th Street near Avenue M in the Flatlands section.
Two other residents and several pets got out safely, including a dog that was rescued by firefighters.
Video from overnight showed firefighters rescuing the injured dog.
The victim was identified as Esther Gee, who neighbors described as a lovable mother of two who also loved her pets.
"That's the great concern is that her animals would have gotten out," one neighbor said. "She would have been very distressed if they hadn't gotten out."
Gee was transported to Beth Israel Mount Sinai Brooklyn, where she died from complications with smoke inhalation.
The fire was under control in just over an hour, but clutter inside the house made things difficult.
Some firefighters were treated for minor injuries.
The damage in the back of the home is extensive, and the fire also spread to the house next door.
"Very nice person, a very good neighbor," one neighbor said. "We say hello to each other and that's about it."
Now, neighbors are mourning the loss of a dear friend.
"We all knew her and loved her," another said. "She's been a neighbor here a long time. We knew her family. We knew her husband. She was a great person, and we're all mourning."
The surviving residents are being assisted by the Red Cross.
The cause of the fire is under investigation.
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