Sabrina Kouider, 35, told a jury at the Old Bailey she cried as her partner Ouissem Medouni had intercourse with her after killing Sophie Lionnet at their flat in Wimbledon, south west London.
She also claimed Medouni waterboarded the 21-year-old au pair in their bathroom, before throwing her lifeless body on a bonfire in September 2017.
Kouider and Medouni, 40, have both said the other was the one being “violent” on the night of the nanny’s death, the court heard on Wednesday.
Each of them admits perverting the course of justice but they both deny murder.
Kouider told the jury she had lied to police on Medouni’s orders after Ms Lionnet’s death, and added under cross-examination: “Everything I done (sic), I did it for him.
“He wanted to have sex with me.
“I’m even shocked to talk about it, it’s embarrassing.”
Orlando Pownall QC, representing Medouni, said: “You suggesting Mr Medouni was insistent on having sex with you when Sophie was lying dead in the bed is nonsense.”
Kouider replied: “I said ‘What are you doing?’ When he finished he said he was so stressed.”
Asked if she was alleging rape, she said: “I was shocked. I was not myself. I didn’t say ‘Don’t do that’ but I was crying while he was doing that.”
Mr Pownall said: “I suggest it is a figment if your imagination.”
Kouider replied: “It’s not my imagination, it’s the truth.”
Mr Pownall suggested the defendants’ cases were “mirror images” of each other.
He said: “You say Mr Medouni had never shown any violence towards her (Mrs Lionnet) prior to 18 September and on that evening he was violent.
“His defence is almost the mirror image of yours.
“He says you were the one that had been violent and were violent in the early hours of the 19th.”
Kouider said: “I reject that. I was not violent.”
Mr Pownall went on: “If one was looking at the two mirror images, would you agree there is an important difference between you and him? First, over many years you have made false accusations against a number of people.”
Kouider said: “I never made a false accusation against anybody.”
The lawyer continued: “Secondly, over a number of years you have shown bad temper and violence towards a number of people.
“The further difference, you always blame somebody else for your problems.”
Kouider denied it.
Mr Pownall suggested that, contrary to what Kouider had told jurors, Medouni was delighted to be “punching above his weight” with her.
She was the one who was “ashamed” of their relationship, telling people he was her cousin or brother, the court heard.
Kouider was so “fiercely jealous, possessive and controlling” that she once set fire to curtains, the jury was told.
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The defendant denied it, blaming a candle for what happened.
The trial continues.