The A92 in Inverbervie was closed for five hours in both directions following the event to allow police to perform examinations.
The other day, 37-year-old Arbuthnott appeared at Aberdeen Sheriff Court and confessed causing Mr. Lyall s death by driving without due care and attention.
Shaking as she signed the paperwork confirming the charge, Arbuthnott resisted tears as she told Sheriff Graham Buchanan she was pleading guilty.
The constable decided to postpone sentence up until next month for background reports.
He also asked for an agreed narrative of the realities to be put prior to him.
He likewise enforced an interim driving restriction.
Court papers specify that Arbuthnott had her vision obscured by the sun prior to the terrible occurrence.
They specify that as an outcome of her impaired vision she did not notice Mr Lyall as he crossed the roadway, nor did she minimize her speed or stop the automobile when she realized she might not see.
Her vehicle was also harmed in the collision, but she was not injured.
It is thought Mr. Lyall was on his method to the beach for a walk when the accident took place near the town s post office.
Neighbors said he was understood for his love of the outdoors and had actually formerly worked as a milkman for Nicolson s Dairy and as a farm worker at close-by Pitcarry Farm before retiring.
Arbuthnott married Christopher, the boy of the 17th Viscount of Arbuthnott, in April 2003.
Her family moved into Arbuthnott House at Laurencekirk in 2011 after the historical estate went through comprehensive repair.
The Arbuthnott household have survived on the estate since Hugh de Swinton was approved the lands of Arbuthnott by King William the Lion in 1188.
His descendant Lord Arbuthnott, the 16th viscount and 33rd laird, died at the age of 87 in 2012.