Clare Nicholls is alleged to have repeatedly punched, kicked, stamped on, whipped and burnt Andrew Gardner, the father of her youngest child.
Under cross-examination Nicholls, 28, admitted she had attacked her partner, 35, but denied she had tortured him to death.
Prosecutor Paul Sloan QC said she had told a pack of lies "from beginning to end" by repeatedly changing her story to play down her role in Mr Gardner's death.
He suffered more than 100 separate injuries, including 21 fractured ribs, in the weeks leading up to his death on March 13 last year, Teesside Crown Court heard.
Nicholls, her brother Simon Nicholls, 24, and her ex-partner Steven Martin, 44, who lived together in Arthur Street, Chilton, County Durham, deny murder.
Yesterday Clare Nicholls admitted manslaughter, a plea not accepted by the prosecution.
Mr Sloan accused all three defendants of being involved in the final, fatal attack on Mr Gardner in the living room of the house they all shared in Arthur Street.
Nicholls maintained that on the day he died she had only punched him twice during a row.
"You accept that you told a pack of lies from beginning to end in all the police interviews, in both March and July?" he asked.
"Pretending Andrew had left the house at about 8pm, pretending he had been assaulted when he was out, returning to the house at about 11pm.
"Complete pack of lies. Pretending the assault occurred away from the house and that others must have been responsible.
"On that occasion, during the final attack, Andrew was pinned to the floor. He was pinned to the floor by Simon and Steven.
"Simon had hold of his arms and Steven was pinning him down as well as punching him in the face.
"It was during this attack that you stamped on his already burnt foot, fracturing it.
"At the time of that attack he was already suffering from 21 rib fractures and it was obvious that he was in need of urgent medical attention.
"Your intention in carrying out that attack was to cause him really serious bodily injury."
Breaking down in tears again to deny Mr Sloan's accusation, Nicholls replied: "I do know one thing that I never wanted to see that man die."
Mr Sloan continued: "You still cannot bring yourself to admit the true extent of what you did that night.
"You cannot bring yourself to admit what your intention was because if you did you would be admitting murder."
She replied: "I did not intend serious harm."
Mr Sloan said Nicholls must have known that Mr Gardner was in excruciating pain in the days leading to his death because of the rib fractures.
"He already had six rib fractures. He is then attacked again, the attack causing another 10 rib fractures," Mr Sloan said.
"So when he is being jumped on, already having rib fractures, he must have been in excruciating pain.
"Miss Nicholls you caused him that excruciating pain because you jumped on him with your knee, a technique you used."
Breaking down in tears, she replied: "I admit to jumping on him once on one occasion.
"The rest of his broken ribs would have been caused by my brother Simon. I did not realise that my knee going into his ribs was going to cause him so much pain."
Mr Sloan also accused Nicholls of "humiliating" Mr Gardner by having sex with Steven Martin in front of him as he lay on the living room floor suffering from fractured ribs.
The prosecutor accused Nicholls of encouraging her three eldest children to attack Mr Gardner.
"You even corrupted your own children. They took their lead from you," he told her.
"Not only were they encouraged to assault Andrew they told of your approval.
"They scratched him with keys as well. They hit him, punched and kicked him, following your lead, and you did nothing to stop them."
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