Emily Arbuthnott, 37, struck James Lyall, 82, while he was walking across the road in front of her car at a zebra crossing on the A92 in Inverbervie in November 2014.
Mother-of-three Arbuthnott, of Laurencekirk, admitted the charge at Aberdeen Sheriff Court.
Sentence was deferred for background reports.
The charge stated the driver failed to slow down or stop when her vision was obscured by the sun and did not notice Mr Lyall as he crossed the road.
He was taken to hospital in an ambulance under police escort but later died.
Arbuthnott, the daughter-in-law of the 17th Viscount of Arbuthnott, was not injured in the crash which happened on 5 November 2014.

It follows an incident in which a member of staff was threatened with what was believed to be a firearm at the shop in Frizington in October.
Paul Roger Farish, 18, of Moor Place, Frizington, appeared before West Cumbria magistrates charged with robbery and possessing an imitation firearm.
He was remanded to appear before Carlisle Crown Court on 7 December.
A second man, aged 19, who was also arrested, has been released on police bail until 14 December.

"Had I been president, Captain Khan would be alive today. We wouldn't have been in this horrible, horrible mistake, the war in Iraq," he said.
The soldier's father, Khizr Khan, said it was a "cruel" remark.
He is campaigning for Hillary Clinton, who is making her first appearance with First Lady Michelle Obama.
The two shared a stage at Winston-Salem in North Carolina.
Introducing Mrs Obama, the former first lady said her voice was needed in this election "more than ever".
Mrs Clinton referred to Mr Trump's ongoing feud with the Khans and accused him of "rubbing salt into the wounds of a grieving family".
Mr Khan's son Humayun was killed by a car bomb in 2004 in Iraq at the age of 27.
Their grief became part of the presidential campaign in July when Khizr Khan made an emotional speech at the Democratic Convention attacking Mr Trump for anti-Muslim rhetoric, as his wife stood next to him.
The Republican candidate's reaction, in which he implied the mother was not allowed to speak up, attracted strong condemnation from within his own party.
Speaking to ABC News in an interview aired on Thursday, Mr Trump repeated his insistence that their son would be alive, but added he believed the soldier was a "great hero".
In response, Mr Khan said: "This is the most cruel thing you can say to grieving parents, that if I was there this would not have happened."
In other campaign developments:
Former Illinois Representative Joe Walsh tweeted: "On November 8th, I'm voting for Trump. On November 9th, if Trump loses, I'm grabbing my musket. You in?"
He later said he was speaking metaphorically about "acts of civil disobedience".
Mrs Clinton's campaign is dealing with more questions arising from hacked emails published by Wikileaks.
The Trump campaign has seized on the latest dump to suggest the line between Bill Clinton's personal income and the donations for the Clinton Foundation has been blurred.
Doug Band, a top aide to Mr Clinton, said in an email that he had solicited donations to the foundation and also generated personal income for him through gifts and paid speeches.
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A motorist has admitted causing the death of a pensioner by driving carelessly on an Aberdeenshire road.
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A man has been charged with robbing a post office in Cumbria.
[NEXT_CONCEPT]
Republican Donald Trump has been criticised by the family of a dead US soldier after saying as president he would have kept him alive.