She said she was in disbelief at the news.
"I didn't believe her and I was saying, 'Are you sure, what's going on?'"
Macdonald later came running into the house.
"He looked really pale and was shaking and had been crying."
The family gathered at the house but Ms Macdonald still did not believe the news.
"I just thought someone must have got this wrong."
Ms Macdonald earlier gave evidence about the time her husband had got up that morning.
Timing is crucial to the case, with the Crown alleging Macdonald shot Mr Guy at his Aorangi Rd home within minutes of 4.43am before cycling back to the family farm to milk the cows by about 5am.
Ms Macdonald told the court the time her husband woke up every morning was consistent for weeks on end, and he told her when it would change.
He set and tested the alarm clock by his side of the bed every night.
Ms Macdonald said she was a light sleeper and she got annoyed when her husband switched on the light in the walk-in wardrobe every morning.
She often did not check the time when that happened because she would have to sit up in bed to see the alarm clock, which was obscured her husband's large pillow.
"Most of the time I didn't want to fully wake up so I'd just roll over."
Ms Macdonald did not know what time her husband got up on July 8, but said he had been getting up about 4.50am "for some time".
She got up about 6.15am that day when she was woken by her four children.
Mr Guy's wife Kylee earlier fought back tears as she told of her son's excitement when he thought his father was coming home on the morning he was killed.
She was woken about 6.30am on July 8 by their two-year-old son Hunter.
Ms Guy said Hunter heard motorbikes and thought Mr Guy was coming home.
She went to the window and saw Mr Guy's silver ute and a large stock truck.
Then she saw police cars and thought farm worker Matthew Ireland may have been run over.
"I didn't think it was Scott," she said.
She and Hunter put on jackets and went outside but a police officer came running up to her.
"He told us to go back inside."
She went into the bedroom and "just sat there" on the bed.
Ms Guy said she was very upset and called a friend to look after Hunter.
On the last day she spent with her husband, Mr Guy had finished work on a cow shed on the property where seven of their chocolate labrador's puppies were kept.
Mr Guy showed his father Bryan the shed that day because he was very excited about the work he had done.
Later that afternoon, she and Mr Guy went shopping at The Warehouse with Hunter and bought a train set for him.
They returned home for dinner when it was dark.
She put Hunter to bed and went to bed herself because she was "knackered".
Mr Guy took a call from a friend and she called out to him to come to bed.
"I was yelling out because I was so tired ... I just wanted to go to sleep."
Mr Guy got off the phone, showered and came to bed.
Ms Guy, who was heavily pregnant with second child Drover, said she slept deeply that night.
"I'm normally a light sleeper but when I'm pregnant I'm a deep sleeper."
Ms Guy said her husband usually awoke to the alarm on his phone but she did not hear it and did not know what time it was set for.
His morning routine was to put on his clothes, which he picked out the night before, before using the bathroom further down the house so he would not wake her and Hunter.
"Then he'd have his coffee and normally check his mail, use the computer."
She was not woken by Mr Guy's ute that morning, and said she hardly ever was.
The trial before Justice Simon France and a jury of 11 resumes on Monday with evidence about Macdonald's relationship with Mr Guy.
