Stacey Jones, of Maple Grove, Whitburn, had seven migrogrammes of the drug in her blood when she drove on A1018 in Sunderland – two-and-a-half times the specified limit of two.
Sunderland magistrates heard the 33-year-old has never been in trouble with the law before police stopped her Toyota Landcruiser on December 12, last year.
Prosecutor Laura Croft said: “The vehicle was stopped because it had no valid MOT. The matter had nothing to do with the manner of her driving. She’s a lady of good character.”
The court heard Jones was told to do a drug test, which she failed, leading to her arrest.
Jones pleaded guilty to driving a motor vehicle with the level of cannabis above the specified limit.
Chris Wilson, defending, said: “She is a long-time user of cannabis. She has done so for medical purposes for a number of years.
“She was stopped by police. The MOT was an oversight.”
Mr Wilson said Jones has a “complex background”
He added: “She had recently given evidence at the crown court, which took a significant toll on her.”
District Judge Roger Elsey said: “Bearing in mind that possession of cannabis is an offence that can be punished by imprisonment and dealing with an excess amount of drug in your system, that is an offence that is punishable by imprisonment, you will not be treated leniently.
“Until today, you were a lady of good character.
“You have now lost that good character.”
Jones was fined £400, with a £40 surcharge and £85 costs.
She was disqualified from driving for 18 months.