Bethany Louise Lucas entered a guilty plea to one count of driving a motor vehicle while over the drug limit when she appeared before magistrates in Northampton in July.
The court heard from the prosecutor that the 27-year-old had been caught out in Weedon Road in Northampton after getting behind the wheel of a silver Volkswagen Golf while over the drug-driving limit on December 3 last year.
An evidential blood test revealed that she had 2.1 microgrammes of controlled class B drug cannabis product delta-9-tetrahydrocannabinol per litre of blood. The legal limit is two microgrammes.
Lucas, of Cradley Close, Hereford, was fined £100 and disqualified from driving for 12 months, with magistrates saying they had taken her guilty plea into account when imposing the penalty.
She was also ordered to pay prosecution costs of £85 and a £40 victim surcharge, which is used to help fund services supporting victims of crime.