Rachael Martin refuted suggestions from the lawyer of her former partner, Barry 'Budgie' McCarney, that she was the killer, not him.
The former couple have been on trial for the last seven weeks at Dungannon Crown Court facing charges arising out of the death of 15-month-old Baby Millie from severe head injuries on 11 December 2009.
During a second day of cross-examination by defence QC Eilis McDermott on Wednesday, 27-year-old Martin was quizzed as to why, during over 15 hours of police questioning, she never once "said anything critical of him".
Ms Martin, from Main Street Kesh, is accused of wilfully neglecting and allowing her daughter's death, claimed police had only asked about her relationship with 33-year-old McCarney, from Woodview Crescent, Trillick, who denies murdering and sexually and physically abusing the youngster.
Ms Martin claimed that she was not asked her "personal opinion of him ... if I was I would have had a lot more to say".
Detectives, she told Ms McDermott, had only questioned her in the same manner as she was questioning her in court.
While the lawyer said it "was obvious" she was answering questions put to her about Mr McCarney, she never put it to detectives that it was "obvious to you that he killed Millie".
Ms Martin said that if she had known about him beforehand, "Millie would still be here", adding that police were only interested in what happened before her daughter's death.
However, Ms McDermott was quick to point out that she was directly asked if she could think of anyone who "could have caused these injuries to Millie".
Ms Martin claimed she "wasn't picking up" on what the detectives meant, as she believed they were talking about anyone beside Mr McCarney who had already been arrested.
Ms McDermott countered with the answer, Ms Martin gave to the police: "The answer you gave ... I can't think of anybody because I didn't have anybody in my house".
"Except Barry McCarney," replied Ms Martin, "he had already been arrested for what he had done to Millie".
It was then that Ms McDermott suggested that it was she and not her client, who was the real killer.
"I want to suggest to you Ms Martin, that the reason why you could not think of who did it, is because you had done it".
"Certainly not ... definitely not ... you know what your client has done," said Ms Martin.
She again refuted the suggestion, telling the court that Mr McCarney "would not have been near my child if I had known what he is and what he had done".
Ms Martin made similar accusations when it was also put to her that she was responsible for causing the multitude of other injuries found on baby Millie following her death.
Ms McDermott suggested to Ms Martin that she "knew exactly why she (Baby Millie) was being bruised".
Ms Martin in turn suggested that she would not have "allowed" her daughter to be injured, and added: "Had I known he (Mr McCarney) would not have been in my house or near my child".
Ms McDermott immediately countered telling her: "I am not suggesting you were allowing it, but causing it".
"Definitely not. Definitely not" Ms Martin maintained, telling the defence lawyer: "You know as well as I do what your client is capable of".
Later she told the court that she had expected to have been a "prosecution witness" in the case against her former lover.
Ms Martin also admitted that when she was arrested the following September it came as a surprise to her.
However, she told the court she had "no explanation" for not telling the police during this second set of interviews that her daughter's fatal injuries must have been caused during the five minutes she was absent.
Equally when Ms McDermott asked Ms Martin for an explanation as to how Baby Millie received her other injuries while she was in the house, she candidly replied: "I can't explain".