Sarah Sands, 32, is accused of murdering Michael Pleasted, 77, weeks after finding out he was charged with sex assaults on two children under 13.
Mr Pleasted was stabbed at his Canning Town home while awaiting trial.
Ms Sands told the Old Bailey she was frightened by his behaviour. She denies murder.
The court heard Ms Sands befriended the pensioner and regularly cooked for him but on learning about the charges went to advise him to plead guilty to avoid the children having to testify.
She said she had drunk two bottles of wine and a small bottle of brandy before visiting Mr Pleasted's flat on 28 November and took a kitchen knife, hammer and wrench with her "for safety".
She told the Old Bailey that when Mr Pleasted opened the door he "smirked" and said his accusers were liars.
Ms Sands told the court: "He was so cold. The man that I thought I knew never behaved like that.
"I was frightened. He was meant to listen to me."
She said she took the kitchen knife out of her handbag and held it to "show him he could not talk to me like that, that I knew him, that I loved him".
She went on: "I just had it in my hand and I poked him with it in the front and that's when we both realised at the same time what had happened and he grabbed me.
"He was frightening me and I pushed him away and I left. That was it."
When asked whether she intended to cause Mr Pleasted "serious harm" she replied, "No. I did not stab him, I didn't".
The court heard Mr Pleasted crawled into his hallway before collapsing and bleeding to death.
Ms Sands handed herself in to police the following morning.
The trial continues.

Football's world governing body acted following the "internal wrangles affecting the FGF that have halted all football competitions in Guinea".
The committee, whose members will be selected by Fifa and the Confederation of African Football, will be tasked to organise FGF elections by 28 February.
Until then the committee will run the daily affairs of the FGF.
The problems have affected Guinea's campaign to qualify for next year's Africa Cup of Nations tournament.
They are third in their group behind Zimbabwe and Swaziland, with only the winners guaranteed a place at the finals in Gabon.
Guinea are also due to host the 2023 Africa Cup of Nations, a decision that was made by Caf in 2014.
A woman stabbed her elderly neighbour eight times after he "smirked" at her when she confronted him about child sex charges, a court has heard.
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Fifa has appointed a normalisation committee to take charge of Guinea's Football Federation (FGF).