READ: Leeds thugs punched and kicked doorman who ejected them from pubLisamarie Willock was told by a judge that she had committed the 'ultimate betrayal' by planning the robbery with her girlfriend Kirsty Tolson.
Tolson was also jailed for three years over the scheme to rob the 79-year-old victim in her sheltered accommodation.
Leeds Crown Court heard the couple had met each other online and formed an 'exceptionally toxic' relationship.
Tolson, 29, of Westfield Lane in South Elmsall, Wakefield, had sent text messages to Willock about how to get access to the building and encouraging her to stab her grandmother.
Willock, 20, of Stocks Rise in Seacroft, Leeds, went armed with a 'large and deadly' knife to the pensioner's residence, managing to get into a communal area but not the flat.
Recorder Joanne Kidd told Willock: "It is terrifying to imagine what would have happened had you done so."
The plan came an end when Tolson got 'cold feet' moments before Willock was about to carry out the attack.
The judge said: "Miss Tolson got cold feet. It is exceptionally lucky that she did because it allowed the emergency services to be called."
The couple pleaded guilty to conspiracy to commit robbery. Willock also pleaded guilty to theft and two counts of possession of an offensive weapon.
Sentencing, the judge told Willock: "You probably considered that she was the most likely person to give into your demands for money.
"That's against the background of her caring for you during a time of great vulnerability when you were pregnant the year before.
"It is the ultimate betrayal."
For the latest news from Leeds Crown Court - join our crime group on Facebook.