That's a question a NSW Supreme Court jury's been left to ponder as it prepares to decide if Natasha Beth Darcy murdered her partner Matthew Dunbar.

The 46-year-old denies giving the Walcha sheep grazier a drug-filled blended drink and then gassing him in bed before his death on August 2, 2017.

Prosecutor Brett Hatfield has suggested Darcy started looking for ways to murder the Walcha farmer by poison in February 2017, citing searches on her iPhone and on a computer.

But Darcy's barrister questioned why her client didn't wash up after supposedly executing the first stage of her quest.

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"The careful and deliberate planning for five months, but she doesn't turn on the dishwasher?" Janet Manuell SC said in her closing address on Wednesday.

"If she had a guilty mind, don't you think she'd turn on the dishwasher?

"(It's) an easy way to get rid of ... this evidence."

Ms Manuell directed attention to photos taken of the kitchen after Mr Dunbar's body was found, showing a "gritty" pink residue down the side of the blender and dishes elsewhere unwashed.

"All she had to do was press the button to turn on the dishwasher - and it wasn't done," Ms Manuell said.

She said jurors may also ask why Darcy didn't just fill the NutriBullet with all the other drugs in the house if she was so intent on killing Mr Dunbar.

"It doesn't make sense that she would moderate the amount and moderate the different types of drugs if the ultimate purpose was to kill Mr Dunbar by the (suicide method)," she said.

When Darcy attended a vet earlier, Mr Dunbar had the time and opportunity to put into effect many of the steps required to put the suicide method into effect, Ms Manuell said.

The Crown says Darcy tried to kill her partner more than once knowing full well she would inherit his multi-million dollar farm, and left "a staged scene to conceal the fact this was murder".

Her police interview was full of inconsistencies and lies she "made up on the run," including her reasons for walking into Mr Dunbar's bedroom the night of his death.

Darcy called triple zero about 2am after she says she walked into the bedroom and saw a bag over Mr Dunbar's head.

The Crown has also tendered evidence of Google searches from Darcy's two phones, neither of which had passcodes.

"Is there a poison that can kill someone but be untraceable at autopsy," was one precise topic searched, the jury was told.

Earlier on Wednesday, Ms Manuell told the jury Mr Dunbar endured a 22 hour wait and "was in hospital not knowing" if his leg would need to be amputated in surgery in July 2017.

"That would be devastating news for anybody," she said.

Ms Manuell said Mr Dunbar "would have been deeply distressed" at the prospect of being a farmer and losing his leg at the knee.

A nurse at Tamworth hospital made a file note that the "patient is anxious + + +" when he was transferred there on July 12, 2017.

The jury was also told the orthopaedic surgeon in Tamworth could not pinpoint the cause of the serious leg infection, although the Crown maintains Darcy injected Mr Dunbar with acepromazine in a "dry-run" in early July.

The specialist gave further good news on the morning of August 1 that Mr Dunbar's condition had improved.

"It was a significant improvement in Mr Dunbar's physical health," Ms Manuell said.

"The question is .... how did he process that information?"

Ms Manuall said later that day in a phonecall to another friend, Mr Dunbar said "I won't walk again" and it was "rather an odd thing" to say.

The trial, which began nine weeks ago, continues on Thursday.

Australian Associated Press with Breanna Chillingworth

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