Her body was found on the ground floor of the house in Hog Lane, Amberley, after the alarm was raised at 16:23 BST on Friday.
The initial call came from an automatic alarm, followed by 999 calls from neighbours, West Sussex Fire and Rescue Service said.
A cause of the blaze has yet to be established.
An elderly woman has died in a fire which started in the living room of a thatched cottage in West Sussex.