A woman accused of causing the deaths of her daughter and another girl in a car crash told a jury she may have "unknowingly" taken cannabis the night before the tragedy.
Anastasia James, a private investigator, has always denied smoking cannabis, although admitted taking a legal high alternative, Mamba, a week before the tragedy.
But giving evidence in her defence, at Leicester Crown Court, she changed her original account and told the jury she may have got her dates "mixed up" and taken what she thought was Mamba, on Friday January 3, 2014.
The following day, at just after 7pm, her convertible Vauxhall Astra spun off a northbound straight stretch of the M1, near junction 19, and hit a tree.
Two passengers, her 14-year-old daughter, Destiny James-Keeling, and her son's 18-year-old girlfriend, Megan Marchant, died almost immediately.
James (37), of Thornton Close, Braunstone, denies causing the death of both girls, by driving without due care and attention, while unfit through drugs (cannabis).
The court heard there was evidence of THC, a cannabis component, in a blood sample taken from James at 1am – but no traces of Mamba.
Two toxicology experts allege the THC level indicated the defendant took cannabis within two hours of the crash - either before setting off to Leicester from a family party in London, at about 5pm, or during the journey.
James, a graduate and former good-parenting co-ordinator, told the court: "I'm really shocked by these (toxicology) results.
"I didn't smoke earlier that day or in the car.
"I wasn't aware I had cannabis in my system."
She disputed a police officer's claim to have smelled cannabis near the wreckage.
She said she was unaware her son, Wade James-Keeling, then 17, who survived the crash, had a 1.5 gram bag of cannabis on him, which was found by the ambulance crew.
She denied having taken any cannabis before or during the journey, saying it would have been morally wrong to have done so.
She said: "I hadn't knowingly smoked cannabis, I thought I smoked Mamba (the night before)
James said she believed her car may have hit debris in the road causing loss of control.
She said: "I remember going straight in the middle of the lane then this feeling of pulling and that's when I'm holding on really tight to the wheel.
"It was like a wobbly sensation and I couldn't stop it from pulling to the right (onto the central reservation).
The car then spun across all three lanes and left the road.
She said: "The steering wheel was spinning out of my hands and I couldn't hold it anymore .
"I was still trying to straighten it, I remember going towards the tree.
"It was shocking to hear I wasn't braking."
Under cross-examination Michael Evans QC, prosecuting, accused her of being "in denial" and urged her to tell the truth for the sake of Megan's family in the public gallery.
James said: "If I was guilty, I would have gone guilty."
