Sheila Lockridge strangled frail Dianne Williamson to death at her home in Gristhorpe, near Filey.
Lockridge, 66, was charged with murder but pleaded guilty to manslaughter and was sentenced at Leeds Crown Court today.
Their 30-year-relationship had become frayed, the court heard, and Lockridge had become aggressive towards Mrs Williamson.
Witnesses said in statements that Mrs Williamson - who was 70, weighed seven-and-a-half stone and was in poor health - suffered various bruises over the years. They suspected she was a victim of domestic violence.
On one occasion, a witness overheard an argument between the couple in which Mrs Williamson pleaded with Lockridge: “Please don’t stab me. Please don’t kill me.”
She rushed into the room to find Lockridge brandishing a kitchen knife and intervened.
On 2 September 2018, the day Mrs Williamson was killed, Lockridge had spent the afternoon in a pub before returning home to Mrs Williamson at around 7pm.
At 7.39pm, North Yorkshire Police received a 999 call from the defendant. She told the call operator her partner was dead.
The prosecution alleged that she didn’t make the call until at least 14 minutes after she killed Mrs Williamson, after ringing other people approximately a dozen times.
Emergency services attended their home in Lodge Gardens, Gristhorpe, to find Mrs Williamson’s lifeless body.
Lockridge later told a police officer at the scene: “I strangled her. She’s dead.”
A post-mortem confirmed that Mrs Williamson died of manual strangulation.
The defendant was arrested and the case was investigated by North Yorkshire and Cleveland Police’s joint Major Investigation Team, which specialises in complex investigations for very serious crimes such as murder, rape and serious robberies.
During police interviews she told officers that Mrs Williamson was violent towards her. She claimed she pinned her down to restrain her, but she never got up. The prosecution said that Lockridge was in fact the perpetrator of the domestic violence.
Lockridge was charged with murdering Mrs Williamson and was due to stand trial for murder.
However, she pleaded guilty to manslaughter – a plea which the Crown accepted – and was sentenced today by a judge at Leeds Crown Court.
After the hearing, Detective Chief Inspector Mark Pearson, who led the case for the Major Investigation Team, said: “This was a brutal and tragic end to a 30-year relationship in which Dianne Williamson suffered at the hands of Lockridge.
“My thoughts are with Dianne Williamson’s family at this very difficult time. No sentence could ever compensate for the loss of their mother and grandmother. However, the jailing of Lockridge today may give at least some closure to those who loved Mrs Williamson.
“I would like to take the opportunity to encourage anyone suffering violence at the hands of a partner to report it to the police.
“North Yorkshire Police have officers trained to deal with domestic abuse in whatever form it may take.
“Any victim will be treated professionally, with respect and compassion. If you do not want to contact the police then independent and confidential support can be provided by IDAS ( Independent Domestic Abuse Services ). They have a 24-hour helpline – 03000 110110.”