Milner, 50, denies killing her second husband Phil Nisbet, 47, by slipping the sedative Phenergan into his evening meal and, while he was heavily sedated, probably suffocating him.
She is also accused of making his death, on May 4, 2009, look like suicide in the hope of cashing in his $250,000 life insurance policy.
Milner also denies attempting to kill him twice on April 15, 2009.
The defence argues Mr Nisbet took his own life.
After the Crown gave its closing submissions this morning at the High Court in Christchurch, in which it described an "overwhelming circumstantial case", the defence had its turn this afternoon.
Defence counsel Rupert Glover told the jury it was a "very sad case".
The whole point of the trial was to determine what really happened, he said.
While the Crown says the trial is about whether Milner assassinated Christchurch delivery driver Mr Nisbet through a fatal dose of Phenergan, Mr Glover said it actually amounted to an assassination of Milner's character by "poisonous testimony" with various people who had "axes to grind".
The "captain of the team" who set out to get Milner was Mr Nisbet's sister, Lee-Ann Cartier, assisted by "first lieutenants", Milner's youngest son Adam Kearns, his then partner Kasey Woodstock, and Mr Nisbet's second wife Karen Porter.
Ms Porter was, Mr Glover alleges, "hot to trot" in vilifying Milner from the outset, while at the same time desperate to secure monies from Mr Nisbet's estate.
But the main antagonist in the case against Milner, was Ms Cartier, he said.
"Even police seem to be seduced by her unrelenting crusade to bring down Helen Milner," Mr Glover said.
During the Crown's case, which called around 70 witnesses, including many former workmates of Milner at Christchurch grounds maintenance firm, GSL, where they nicknamed her the Black Widow, much of the evidence had been "orchestrated" by Ms Cartier, he said.
"It can't have escaped you that from the very outset, the police have tried to bend over backwards to portray the most negative aspects possible of Mrs Milner's character."
The result was the "cardboard cut-out of the Black Widow", he said.
The trial continues.
Justice David Gendall sum up for the jury tomorrow morning before they begin considering their verdict.
