Thibault's lawyer Marc Labelle, tried to invoke royal privilege last month to quash fraud charges against her, but the court rejected the argument and ordered a trial. Labelle argued that the Crown's prosecution cannot prosecute the Crown or its direct representative.
He said his argument centres on an old and little-used common-law principle that states "the Queen can do no wrong."
The former lieutenant-governor is expected to file for an appeal.
In September 2009, she was accused of misspending public money during the decade she was in office. She pleaded not guilty to two counts each of breach of trust, fraud and creating false or counterfeit documents.
Labelle argued that the excessive spending Thibault was charged with was linked to her functions as lieutenant-governor. He said the Superior Court should have ended the procedures during the preliminary trial.
The Crown countered that Thibault has privilege only when she is acting within her functions as lieutenant-governor, and that criminal acts are never part of the lieutenant governor's functions.
On Aug. 27, the Superior Court ruled that the judge presiding over the trial could determine if the royal immunity argument was valid.
A court date is expected to be fixed for Dec. 3.