A former associate of Cook County Judge Jessica Arong O’Brien pleaded guilty Friday to her role in a $1.4 million mortgage fraud scheme and is expected to testify at O’Brien’s criminal trial next month.

Maria Bartko, 50, of Streamwood, pleaded guilty to one count of mail fraud affecting a financial institution.

U.S. District Judge Thomas Durkin put off setting a sentencing date until after Bartko’s anticipated testimony against O’Brien, who is scheduled to go to trial Feb. 5 on mail and bank fraud charges stemming from the same alleged scheme. O’Brien has pleaded not guilty.

Federal…