TORONTO -- A woman who helped her boyfriend inflict unimaginable sexual and physical torture on her ex-husband was a "gullible, easily-controlled" simpleton who couldn't save him, a sentencing hearing was told.

Psychiatrist Derek Pallandi testified Monday that the woman's low intelligence, naiveté and stress handcuffed her from sparing her former husband from a litany of abuse at the sadistic hands of her boyfriend, John Siscoe.

The woman, 31, has admitted she was an accomplice as Siscoe perpetrated three months of torture against her ex-husband, 40, while the trio shared an apartment in the fall of 2009.

The three met in B.C. and moved together to Toronto in September 2009.

The identities of the woman and the victim are covered by a publication ban.

In January, she and Siscoe, 41, pleaded guilty to aggravated assault and sexual assault causing bodily harm in a reign of terror from Oct. 31, 2009, until Jan. 19, 2010, when police rescued the man.

The victim suffered five fractured ribs, two collapsed lungs and his black and blue face was swollen to three times its normal size.

The severely malnourished man endured razor slicings, head-stompings, sodomy and hammer blows, court heard.

Siscoe would cauterize the victim's wounds with stove-heated knives, court heard.

The woman shouted at the victim to "shut up" when Siscoe set her estranged spouse's genitals ablaze with lighter fluid in December 2009.

The woman was pregnant with Siscoe's son, who was born in March 2010. She said she feared authorities would seize her child after he was born if police discovered the victim's horrific injuries.

Halfway through the violence, Siscoe said that "burning and beating the victim was starting to turn him on," court heard.

Siscoe once pinned the victim's lips together.

Pallandi stated in his report that the woman couldn't protect her estranged spouse because she "simply lacked the intellectual and adaptive resources to reason an appropriate course of action."

Diagnosed as "mildly mentally retarded," she understood that the abuse was wrong and illegal. But she thought if she reported it to police, then Siscoe would make good on his threats to kill the victim's elderly parents in B.C., stated Pallandi.

Barring bizarre circumstances, she's not a threat to repeat this crime, the psychiatrist told Justice John McMahon.

Crown attorney Paul Leishman said the prosecution is seeking a "significant penitentiary term for the woman.