Convicted burglar Paul Prause, 65, pleaded guilty to murdering former seamstress Rosina Coleman at her Romford home in May.
Judge Philip Katz QC jailed him for life with a minimum term of 22 years.
He described the wounds inflicted on the vulnerable victim as "sickening".
He told Prause: "Your attack with a hammer was brutal and sustained long enough for her to have defensive wounds. Her terror can only be imagined. There were at least 11 blows with severe force."
The Old Bailey heard how Prause had worked for Mrs Coleman as a gardener for about six years.
On May 15, he donned latex gloves and battered her with a hammer in her bedroom before calling police, claiming he found the body when he arrived to mow the lawn.
He later admitted killing Mrs Coleman, claiming he acted out of anger at something she said.
Prosecutor Duncan Atkinson QC said: "He said that he had been under pressure for some time and if it had not been Rosie that day someone else 'would have got it'."
He said the defendant had set about staging the scene of a burglary before police arrived.
The blood splattered bedroom was ransacked with drawers pulled out.
Mr Atkinson said: "Significantly, a valuable ring that he had taken from Mrs Coleman was recovered from his home, raising the possibility, given the financial debts under which he was labouring at the time, that there was a financial motivation for his actions leading up to the confrontation with Rosie Coleman in which he killed her."
The murder weapon was recovered from the River Rom, where Prause had thrown it after the killing.
When Prause's home in Romford was searched, a white gold diamond ring solitaire twist was found on top of a brick inside the garage.
The ring, belonging to Mrs Coleman, had a retail value of up to £7,000.
At the time of the killing, regular gambler Prause was in debt, the court heard.
Mrs Coleman was described as a "much-loved" mother, grandmother and great grandmother.
Outside court, Mrs Coleman's daughter Sharon Thomas said she lived her life "to the full".
She said: "We as a family have been robbed of our queen. We feel robbed through mindless greed.
"This has left a hole in our family which will never be filled."
Mrs Coleman had two children, five grandchildren and eight great-grandchildren and was "loved by everyone", she said.
The victim, nicknamed Bubbles by her great-granddaughter, was fit and "strong in mind" and would have lived to reach 100, if it were not for Prause's actions, Ms Thomas said.
On her killer, she added: "I could not wish him any more damage than he has done himself. I'm a Christian. I've got to find a way of forgiving him. I don't think I'm ready for that.
"I do not wish him dead or anything like that. That would be too easy. He's got to spend every day remembering what he has done. That's the punishment."
Detective Chief Inspector Paul Considine, of Scotland Yard, said: "Rose has been described to my investigation team as a well-respected and independent lady who loved gardening and making dresses, and attended the Royal British Legion club on Saturday nights."
She became the victim of a "despicable and ruthless murder by someone she trusted", Mr Considine said.
He added: "In interview he said he became angry after she made a jokey comment to him but the police investigation and the prosecution maintain that his motivation that day was to steal Rose's precious jewellery and when she challenged him, he murdered her."