One of the jurors injured herself on the way to the jury room at the Sydney Street Courthouse and had to be taken to the hospital.
She was replaced and the jury is now made up of six men and six women.
MacKenzie is being retried for the death of 29 year old Patrick Thomas in March of 2010 on Alma Street.
The Court of Appeal ordered a new trial after concluding the judge at the original trial erred in his instructions to the jury.
The first trial heard plenty of testimony about MacKenzie and Thomas having a volatile and often violent relationship.