Mrs Lyons-Friesen said she and her husband hosted the couple for dinner at their Calgary home. Afterwards, the four went to Beckett's and Mrs Letts-Beckett's motorhome, which was parked in a nearby lot.
After a few minutes of small talk, Mrs Lyons-Friesen said, things took a turn.
"The conversation changed abruptly," she said.
"Laura shared some things that were a problem in their marriage -- problems they were having -- and opened up. She shared a little bit, he shared a little bit."
Mrs Lyons-Friesen said the situation quickly worsened.
"It escalated from that into the most horrific argument I've ever seen with a married couple," she said.
"She said that he had physically abused her. He denied it. She said, 'Peter, you know you did'.
"He called her names. He called her a cow over and over and over. 'You're just a cow, you're just a cow'. He said, 'You're not nearly as good as my first wife was. I should have stayed with her'.
"It was just a barrage of things."
Defence lawyer Donna Turko suggested Beckett was saying "ow" not "cow". Ms Turko also implied the term "ow" was New Zealand slang.
Beckett and Mrs Letts-Beckett separated a short time after the October 2007 fight. She went to police alleging physical abuse, but charges were never laid.
Mrs Lyons-Friesen said she and Mrs Letts-Beckett communicated often during the separation, but their relationship changed when Mrs Letts-Beckett and Beckett reconciled in early January 2008.
The cousins saw each other at a family gathering in June 2008 and spoke briefly. Mrs Lyons-Friesen said that was the last time she saw Mrs Letts-Beckett.
Mrs Letts-Beckett was raised in a family that followed a conservative Christian order called Plymouth Brethren.
Ms Turko asked Mrs Lyons-Friesen about the processes of shunning and ex-communication.
Mrs Lyons-Friesen denied she was shunned when she split up with her first husband, who was also Plymouth Brethren, but did acknowledge certain family members and members of the church were not happy.
"There were family members who were disappointed in the change in family dynamics," she said.
"I knew they didn't think this was something they were approving of."
Mrs Letts-Beckett's mother, Beth Letts, was the first witness called by the Crown. She admitted to disapproving of her daughter's two boyfriends prior to Beckett because they had each been previously married.
Beckett and Mrs Letts-Beckett kept Beckett's prior marriage a secret from her family until the couple separated in 2007.
Mrs Letts admitted in court that she had little contact with her daughter after she reconciled with Beckett, citing stress and a medical condition.
During her cross-examination of Mrs Letts on the first day of the trial, Ms Turko implied Mrs Letts-Beckett was thrown into depression after having been shunned by her family -- a notion Mrs Letts denied.
The Crown expects to call 50 witnesses in the trial, which continues this week.
