Sarah Burke suffered a fractured jaw and cheekbone in the attack early on Sunday and died without regaining consciousness.
The intruder broke into The Green, a Cornwall County Council residential home in Redruth, where Mrs Burke was the oldest resident. She was due to celebrate her 100th birthday on 14 January.
The motive for the attack is unknown and there is no evidence of anything missing from the room, which is on the ground floor of the building.
A police spokesman said the victim suffered 'multiple facial injuries which may have been inflicted by fist, boot or a weapon'. He said there was a strong possibility that her attacker was heavily bloodstained as there was blood on the walls, ceiling and bedclothes.
Dr Bill Hunt, a Home Office pathologist, was carrying out a post-mortem examination at Treliske Hospital, Truro, to establish the cause of death.
Police said a care assistant had checked on Mrs Burke, who was immobile, at 3am on Sunday. She was found dead at 6.45am. They believe the intruder may have got into the home through a window, entered her room and attacked her before leaving through her window, where the curtain had been damaged.
Mrs Burke, a former mill worker, moved to Cornwall from her native Lancashire in 1958 to be near one of her four daughters. She was widowed in 1962.
One of her daughters, Doreen Leverton, 63, of Mount Hawke near Truro, yesterday appealed for people to 'spare a minute from their Christmas preparations' to try and recall anything which could help the police.
'You always expect a parent to die sometime, but not like this. It was a horrendous attack on a little old lady in her bed and the terrible thing is whoever did it could strike again.'
She said her mother's mental capabilities had recently deteriorated and she had the 'mind of a child'.
Mrs Leverton said her family and the residential home had been preparing for Mrs Burke's 100th birthday party.
A spokesman for Devon and Cornwall police said extra officers were being drafted in to help inquiries.
Detectives were carrying out house-to-house inquiries close to the home yesterday.