The Montreal woman accused of killing three teenage daughters and her husband's other wife took the witness stand in her own defence Monday to dispute claims she had rocky relationships with family members.

Tooba Yahya, 42, her husband, Mohammad Shafia, 59, and their eldest son, Hamed, 20, each face four counts of first-degree murder in the deaths of the Shafia sisters — Zainab, 19, Sahar, 17, and Geeti, 13 — and Rona Amir Mohammad, 52, Shafia's other wife in a polygamous marriage.

Their bodies were discovered in a car submerged in a canal near Kingston in July 2009. The cause of death was determined to be drowning.

The defendants, who have been jailed since their arrests in 2009, have pleaded not guilty to all counts.

Within minutes of her testimony, Yahya broke down in tears, causing a brief delay in proceedings, as she recounted her relationship with her husband's other wife. Yahya said she felt sorry for Rona Amir because she wasn't able to bear children, adding she even gave the woman her daughter Sahar to raise.

The high-profile trial began in October in Kingston and was adjourned for three weeks over the holidays. It recommenced Monday morning in what is expected to be the final two weeks of arguments.

The family moved to Montreal in 2007 after fleeing Afghanistan several years earlier.

The Crown contends the victims were killed because the girls' behaviour and boyfriends brought shame on the family in the eyes of the accused.

After taking the stand, Yahya maintained she had a good relationship with Rona Amir, despite the fact that Amir had written in  her diary that Yahya "separated Shafie from me forever" and "took the power of the household from me."

Yahya testified she and Shafia never limited the other wife's movements or her finances.

Diary 'didn't have any meaning for us'

She told the court she found the diary while cleaning the house after the deaths.

"It didn't have any meaning for us. I just put it there on the table. There was no need for me to hide that or burn that," she told the court.

Yahya also testified that when her husband returned from a business trip, she would not tell him about any disciplinary issues with the children, "because of his habit to make small things — he used to make it a big thing."

She said one time she saw Shafia strike the children, but that the parents would always try to verbally discipline them or take away their allowance instead.

Yahya testified the Shafia children did not fast for Islam's holy month of Ramadan. She said her husband didn't want them to because he was concerned it would "stunt their growth."

She said she taught the children about their religion, but did not force it on them. The defence showed a number of family photos and noted that most of the female members seen in them were not wearing the Islamic hijab head-covering.

Daughter acted out when 'she wanted expensive things'

The defence later questioned Yahya about another claim in the diary, where Rona Amir writes about a suicide attempt by Sahar after an argument. In the diary, Rona describes the girl swallowing the preservative that comes in purses and Yahya dismissing it, saying, "Let her kill herself."

Yahya presented a different version of what happened. She didn't deny that Sahar swallowed the preservative, but said she spit it up and refused medical attention. She said Sahar frequently said, "I'll kill myself" when she didn't get her way.

Yahya said one of Sahar's teachers offered her an explanation for the girl's behaviour. She told the court the teacher said, "Because you love her a lot, she is abusing this emotion whenever she wants expensive things."

Earlier in the trial, court heard that on the day of the drownings, the family had been returning to Montreal following a trip to Niagara Falls, Ont. They had stopped at a motel in Kingston for the night.

The defence has maintained the deaths were an accident that happened after the elder daughter, Zainab, took the keys to her father’s car and drove it into the Rideau Canal in June 2009.

Court has already heard testimony from dozens of witnesses, including family members, teachers, social workers, police officers and technical experts.

Jury members have also heard a series of wiretap conversations between the accused recorded secretly by the Kingston police.

With files from The CBC's Dan Halton and Melinda Dalton