Eimear Cook lied in her evidence about two meetings she had with Rebekah Brooks, the former editor's defence counsel told the court.
Cook admitted under cross-examination that a meeting at a friend's home had probably taken place in September 2005 - 10 months later than she had initially claimed.
Jonathan Laidlaw QC also questioned Cook's police statement in which she said Brooks had told her about being accused of assaulting her then-husband Ross Kemp.
He told the court: "Mrs Brooks was not the subject of an accusation of assault, or the subject of the police being called until November 2005 ... Not only did it not happen, it could not have happened."
Cook replied: "I did not make it up ... I have no grievance against Mrs Brooks personally."
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Marjorie and Michael Cawdery, both 83, are understood to have been stabbed to death in a killing their family called "incomprehensible".
Detectives have launched a murder investigation following the shooting in Brent, north west London on Friday night.
Hot and humid throughout the Bank Holiday Weekend.