During the trial, it emerged that Pleasted - who also went by the name of Robin Moult - had 24 previous convictions for sexual offences between 1970 and 1991.
On the evening of November 28, 2014, she armed herself with a knife and repeatedly stabbed Pleasted. After the "determined and sustained attack", he crawled from his living room and collapsed in his hallway where he bled to death.
Within hours, Sands handed herself into police, telling an officer: "Who houses a f------ paedophile on an estate, like, seriously? He was, like, asking for trouble."
She explained she had thought Pleasted was just a "nice old man", adding: "He's f------ harmless now, ain't he?"
At the time, Pleasted was on bail awaiting trial at Snaresbrook Crown Court on two charges of sexual assault on two children aged under 13. Police were investigating a further allegation he had abused a third boy.
The Old Bailey heard that Pleasted had a string of convictions for sexually assaulting boys between 1970 and 1991.
The serial child abuser had previously served sentences of between nine months and six years for sex crimes which included indecent assault on a male over 16; indecent assault on a male under 16; indecent assault on a male under 14; and another sexual offence.
But before the fresh allegations emerged, Pleasted had become a well-known community figure running a bric-a-brac stall from a local shop, the court heard.
Sands had befriended him and used to go round to his flat with home-cooked meals.
She sobbed in the witness box as she insisted that she did not mean to hurt Pleasted when she went to his flat armed with a knife on the night of the killing after drinking a bottle of brandy.
She told jurors she had gone there to plead with him to admit his crimes and spare his young accusers from having to go to court.
But when he answered the door, he ignored her request and just "smirked" as he told her the boys were all liars who had ruined his life.
Sands said during her trial: "I was frightened. It was not how it was meant to go. He was meant to listen to me."
The sentence increase was announced by Lady Justice Macur after the court heard argument on behalf of Attorney General Jeremy Wright that three-and-a-half years was "insufficient".
A spokesman for the Attorney General's office said in a statement after the decision: "Our office received a great deal of correspondence in regards to this highly emotive and sensitive case.