The Supreme Court of Canada heard arguments Thursday on whether victims of domestic abuse can hire a hit man to kill their partners, a controversial issue which tests the limits of the defence of duress.

The case involves a Nova Scotia woman, Nicole Doucet, who tried to hire an undercover RCMP officer to kill her husband Michael Ryan.

The high school teacher was arrested in March 2008 and charged with counselling to commit murder.

She was acquitted of the charge two years later after the Nova Scotia Supreme Court accepted her argument that she thought she had no other way out of an abusive 15-year marriage to a man who repeatedly threatened her and her daughter.

At trial, her lawyer successfully used the criminal defence of duress, arguing that she had no other avenue of escape from the situation. Duress is usually used when someone involuntarily commits a crime after being threatened by another person.

The Nova Scotia Court of Appeal upheld the ruling, saying the marriage amounted to a "reign of terror."

The Supreme Court recognized battered woman syndrome in a landmark 1990 case. It outlined how a woman in an abusive relationship who kills her partner can use the Criminal Code’s self-defence provisions to argue for an acquittal.

But Nova Scotia prosecutors say the self-defence provisions and the defence of duress were incorrectly applied in this case.

During Thursday's proceedings, the prosecutor's office argued that the defence of duress has been mixed up with the defence of self-defence, CBC's Leslie MacKinnon reported from the court. They argued that a future jury would find it confusing to deal with trying to filter which defence applies to which case.

The justices asked William Delaney, of the Public Prosecutor's Office, whether they should find that Doucet should have used the defence of self-defence and acquit her anyway. Delaney said this would be unfair and that different witnesses would have been called, MacKinnon reported.

Delaney also argued that the "air of reality" was not there for the duress defence and that the two had been separated for seven months and that Doucet was well on her way to independence.

He also said Doucet had an avenue of escape  — a transition house  —  something the trial judge had rejected.

But Joel Pink, a lawyer representing Doucet, argued that the trial judge accepted all the facts and  that she didn't tell police about the sexual assaults because police would have gone to her husband and he would deny it.

He said the breaking point was when  Ryan showed up at the school where Nicole Ryan worked. Less than a month later she looked for a hitman.

With files from CBC's Leslie MacKinnon, Alison Crawford and the Canadian Press