Milner also denies attempting to kill him twice on April 15, 2009.
The defence argues Mr Nisbet took his own life.
This morning, Crown prosecutor Brent Stanaway spent two hours summing up what he said amounted to an "overwhelming circumstantial case".
Office administrator Milner had spoken so frequently about "getting rid" of her delivery driver husband, openly discussing methods and poisons, that she eventually "talked herself into it", he said.
Former colleagues, who dubbed her the Black Widow, told how Milner constantly bitched about Mr Nisbet, asking if rat poison would kill him.
After his death, she made a hysterical 111 call which has been played in its 11-minute entirety to the jury.
The first police officers on the scene questioned whether her grief amounted to "acting".
But her defence counsel Rupert Glover today said: "Only an actress the calibre of Meryl Streep could put on a performance like that," adding that the 111 call was a powerful piece of evidence.
Multiple suicide notes, two cards, and a suicide text were unearthed by Milner in the hours, days, and weeks afterwards, the court has heard.
Mr Stanaway said that just doesn't add up.
"How many suicide notes can one man leave, and why?"
The first note she claims to have found amounted to a "Mills and Boon" piece of fiction, he said.
The note was shown to various family members and friends who say it originally contained a forged signature of 'Phil'.
Her own son Adam Kearns gave testimony against her, claiming that he caught her crushing up pills on the day she's alleged to have twice tried to kill Mr Nisbet.
But Mr Glover rubbished his evidence.
"Adam's evidence here, as elsewhere, is a pack of lies."
Mr Glover argued it was not a case of murder by poison, but rather an assassination of Milner's character by "poisonous testimony".
Instead of relying on circumstantial evidence, he urged the jury to look at the science.
Medical expert and defence witness Professor Ian Whyte thought the most likely number of 25mg Phenergan tablets taken by Mr Nisbet was 45-50.
Experiments by police and other witnesses reported that food tasted extremely bitter and barely edible when more than 25 such pills were used.
The Crown have tried to suggest as few as 14 pills would have worked in knocking out Mr Nisbet.
"So, where does that leave us?" Mr Glover asked.
"With the alternative which Crown says is suffocation. But before a person could be suffocated in those circumstances they would have to be in a coma, not just asleep."
Forensic pathologist Dr Martin Sage said there was no evidence either way of suffocation.
Mr Glover concluded: "It would be hugely dangerous to convict this woman on such an orchestrated body of contentious evidence."
Justice David Gendall will sum up for the jury tomorrow morning before they retire to consider their verdict.
