The legal limit for adult drivers is 250mcg.
"That is an extraordinarily high level and it is certainly isn't surprising you had difficulty driving on this occasion,'' Judge Farnan said.
Any driver with more than 250mcg in their system gets ticketed.
Those over the criminal limit of 400mcg are required to go to court.
O'Reilly told police she was taking her child to school.
She said she had not consumed any alcohol that day but had "two or three'' bottles of wine the previous evening and had not eaten any food.
Judge Farnan said the pre-sentence report made it clear she was remorseful.
She was struggling to cope with a recent separation and also had a health issue.
She accepted responsibility and said it was stupid to drive on that occasion. But it was concerning she did not fully accept she had an issue with alcohol, Judge Farnan said.
"You clearly need all the assistance you can get.''
Judge Farnan said it was necessary to denounce the offending and deter others.
O'Reilly was sentenced to nine months' supervision, with conditions she attend and complete any alcohol and drug programmes, treatment and counselling to the satisfaction of a probation officer. She was also sentenced to 150 hours' community work and disqualified from driving for 12 months.
Child, Youth and Family was notified when she was convicted in June.
O'Reilly had been granted interim name suppression but did not apply for permanent name suppression.