Monika Fourie poured searing hot water from a cup and kettle at her alleged victim as she sat on the sofa in Plymouth, Devon, a jury was told.
Hannah Stokes, 24, had started an affair with Mrs Fourie’s husband Walter just weeks earlier.
She suffered “terrible burns” from the hot water — which was boiled when “eerily calm” Mrs Fourie pretended to make a cup of tea, Plymouth Crown Court heard.
Walter Fourie was upstairs after being told to leave the room so his wife could interrogate his mistress over her age and whether she had kids, according to prosecutors.
Fourie, 34, has denied causing grievous bodily harm with intent in October 2015 — but has admitted the alternative charge of causing GBH without intent.
Jurors were told Ms Stokes suffered burns to her chest, neck and back and had undergone surgery for a perforated eardrum.
Mum-of-one Mrs Fourie had been going through marital problems with her South African-born husband before the affair began in September 2015.
Mr Fourie had come clean about his new relationship and believed his marriage to Monika was over.
On the day of the alleged attack, it is claimed Mrs Fourie pretended to make a cup of tea after walking in on Ms Stokes on the sofa of her marital home.
After allegedly scalding her victim, she then chased her out of the house while pulling her hair, jurors heard.
Giving evidence, Ms Stokes fought back tears as she told the court how she would have to live with the consequences of her affair for the rest of her life.
She said: “I saw someone full of rage. She was hunting me down. I know we both did something wrong in this situation and the reality is that I had an affair.
“But now I am out of the shock, I know I did not deserve what I got.
“I would have to be sick to exaggerate the hell I have been through.
“I have to live with this every day for the rest of my life with what she did. She had snapped as I was in her house.”
Mrs Fourie, who suffers from anxiety and depression, has argued she has no memory of the events of that night, the prosecution said.
Her trial continues.
