The inquest is taking place into the deaths of two sisters killed in a road accident on the A47 near Wisbech in December 2012.
Ten-year-old Tamzin Portor and seven-year-old Jessica were on their way to watch a film in Peterborough as a Christmas treat.
They were back seat passengers in a Ford Focus driven by their step mother Marie Easter. Their father Alan was a front seat passenger.
Marie Easter told the Coroner she had to swerve to avoid a car coming in the opposite direction. She said she lost control and knocked herself out. She could not remember anything else.
The car overturned and the girls were killed.
Earlier this year she was given a suspended prison sentence after admitting causing the deaths of the girls by careless driving.
The girls' father Alan Portor said he was on the phone and did not see the car that Marie said she was forced to avoid, but believed her - even though others had claimed it was not true.
He said he had checked with the children that they were wearing seat belts, and they said 'yes'.
The inquest continues.