Maxine Carr insisted to police she invented a false alibi for then boyfriend Ian Huntley, the Soham murder trial has heard.
Ms Carr says she told Mr Huntley what to write on a 'crib card'
She told police it was her idea to claim she was in the house she shared with Mr Huntley on the day Holly Wells and Jessica Chapman disappeared.
Ms Carr also falsely claimed she wrote a "crib card" detailing the alibi.
Ms Carr denies helping an offender and conspiring to pervert the course of justice and Mr Huntley denies murder.
Ms Carr was staying with her mother in Grimsby on Sunday 4 August this year, the day the girls disappeared, but she initially told police she had been at 5 College Close in Soham, Cambridgeshire, the house she shared with Mr Huntley.
It was in the bathroom of their house on that date that Mr Huntley says the girls met their deaths - Holly when accidentally falling into the bath and Jessica when he covered her mouth to stop her screaming.
In a police interview after her arrest she said Mr Huntley had told her to tell
police the truth, but she had decided to lie to "protect him from the past".
She told officers she did not want a false allegation of rape made against him in 1998, that he had told her about and had triggered a nervous breakdown, dragged up again.
Asked if he had made her lie, Ms Carr replied: "No, he hasn't made me lie to anybody. I've done it of my own accord."
Asked if it was to protect him, she agreed, explaining it was "because he hasn't done anything wrong and whatever ... I mean, I know you've gone through loads of stuff earlier on in the interview but I still stay at the same position that to me he's done nothing wrong.
"I love him and this is just all wrong."
When a photocopy of the "crib card" - detailing key times of an alibi for Mr Huntley - was shown to Ms Carr by police she initially insisted she had written it before conceding it was in his handwriting.
The card read "4.55pm, got in bath, 5.40 to 5.45pm, dog home, 6.15pm, girls arrive, 6.55pm, came down to put on tea".
Ms Carr told police it had been her idea to say she was in the bath, reasoning "I couldn't exactly say I was on the front doorstep, could I?"
After admitting it was written by Mr Huntley she said: "So he wrote it down 'cos he said 'if you're gonna carry on lying like this you're gonna have to remember what you're lying about'."
After further questioning she told officers: "He had the piece of paper and I told him the various times and what I was doing at that time.
"He just wrote it down, he didn't write it down himself out of his own head."