She committed perjury when she lied under oath during the trial.

To lie under oath in court

lie under oath

If a judge is acting in his/her capacity of a judge, he/she does not offer testimony and therefore cannot perjure. However, if the judge is testifying as a citizen before another court, he/she is subject to the same rules of perjury as any other person.

The verb form of perjury is "to perjure," which means to willfully tell a lie while under oath in a court proceeding.