A woman caught driving at Rolleston, west of Christchurch, with a high breath-alcohol level while her two young children were in the backseat admits it was "just stupidity" that she was driving.

Melanie Susan Trebilco, 38, has already "taken steps to deal with her alcohol situation", defence counsel Donald Dickson told the Christchurch District Court on Monday.

Trebilco pleaded guilty before community magistrate Leigh Langridge to a charge of driving with excess blood alcohol after being caught at a random stop in Tennyson St on December 9.

Her alcohol level was 1157 micrograms of alcohol to a litre of breath. The legal limit is 250mcg.

Police said at the time that she refused to let officers escort her children to the station after the traffic stop. She told them she would not put her children, aged 3 and 9, at risk in the back of a police car without child restraints.

When she was stopped at 3.12pm, police noticed a strong smell of alcohol on her breath. She told police she had "only had two glasses of wine with the girls at lunchtime".

Police commented at the time that she had been caught driving at more than four times the legal limit of 250mcg in an area where many children were leaving Rolleston Primary School and a daycare centre, crossing the road at pedestrian crossings or on the footpath, and there were other cars with parents picking their own children up.

Dickson said she had been stopped at random and not because of bad driving. She had no previous convictions for any offences and had entered an early guilty plea.

"She says it was just stupidity that she was driving."

Langridge said it was an extremely high level, but she noted Trebilco had not been driving badly, co-operated with police, pleaded guilty and had "self-referred for the appropriate assistance".

She imposed a fine of $1000 and disqualified her from driving for eight months, but warned Trebilco: "You have to know that if you come back for another similar offence, the penalty is going to be far more severe."