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Defence lawyers have challenged Macsyna King, mother of Chris and Cru Kahui, over her claims that she was not at home when the twins were fatally hurt, saying phone records prove she returned to the house and "lost it".
Ms King, 31, was giving evidence at the Auckland High Court trial of her former partner Chris Kahui who the Crown alleges murdered the babies when they were three months old.
He denies the charges and says Ms King was the killer.
During a dramatic exchange with Kahui's lawyer, Lorraine Smith, Ms King denied returning to her Mangere home the night police believe the fatal injuries were inflicted.
She claimed she was with her sister Emily and they never went near Mangere. But Mrs Smith told the court cellphone records proved Emily King was in Mangere just before 8pm.
Mrs Smith said Ms King had returned home because she was only supposed to stay away for a few hours.
After being dropped off by her sister, she become enraged on finding Kahui had left the house to visit his mother.
"You returned home and you lost it," Mrs Smith said.
Ms King said that was "absolutely not true".
Mrs Smith said: "I put it to you that you did something terrible to the twins."
Emily King returned to Mangere to pick her sister up, the lawyer said.
"What happened to make Emily suddenly go back?"
Mrs Smith said Ms King had two chances to hurt the twins that day, one at night and the other earlier that morning.
Ms King was also forced to deny claims she covered bruises on the babies' faces with makeup and that she knew the babies were badly hurt but pretended she knew nothing.
"My evidence is that is bullshit," she said.
She tearfully and angrily denied she bathed the babies in an effort to make them look clean before she went to the doctor.
Mrs Smith: "You pretended for as long as possible ... you knew there was something wrong with the babies."
Ms King denied telling her sister in Maori that a "woman with evil spirits" had hurt the twins.
Mrs Smith said Ms King then back-tracked telling her sister that Kahui was the one who hurt them.
"You were talking about yourself weren't you? And then you back-pedalled and said it was Chris."
Crown prosecutor Richard Marchant asked Ms King if she had ever smoked the drug P and she replied she had - a week before her babies were hurt.
She said it was the only time she had taken P and denied she took it because she was notcoping with caring for the twins.
She rejected suggestions she drove the twins anywhere while high on P but said she did care for them while under the drug's influence.
Earlier, she defended herself from accusations she had not been to the hospital to visit the critically ill twins.
She told the court the reason for staying away was that she could not bear to see her babies dying.
"They were on their deathbeds ... I just could not physically look at my sons in that state."
Her cross-examination continues today.
