Ms Scott built on her existing 50 per cent stake in Elgin-based Gleaner by acquiring the remaining shareholding from Mr Young, her uncle, for an undisclosed sum.
Based on its most recent accounts at Companies House, which show pre-tax profits of £889,351 for the year ended December 31, Mr Young's stake will almost certainly have been worth several million pounds.
Ms Scott inherited her initial shareholding following the death of her father in April 2010.
A "trusted confidante" of the Scotts is now undertaking a review of the company, which turned over £125 million in its most recent financial year.
The review is expected to lead to a three-year plan to grow the business organically and potentially by acquisitions, with the firm stating his wish to expand in Scotland and the north of England.
Some 20 staff are expected to be added to its current 180-headcount, however at this stage the company has still to specify the exact roles it will look to fill.
Mr Scott, a partner in law firm McClure Naismith, said the agricultural and industrial fuel supply sectors hold the biggest opportunities for growth. But he insisted the company was in no hurry to add to its estate of nine petrol forecourts.
Mr Scott said: "We're not hugely excited by necessarily acquiring forecourt businesses. If it is something that is profitable and sustainable, then yes we will look at it.
"But I think all of the independent operators would have to acknowledge that competing with the supermarkets is not the easiest thing.
"We will look at whatever possibilities come our way, but I would think it is perhaps more inclined towards non-forecourt business, certainly in the ownership sense."
While Mr Scott hopes the deal will result in a more prominent role for his wife at the forefront of the business, he was emphatic that David Todd will continue as managing director. He also said the couple had been motivated to complete the purchase by a desire to "look after" staff and pensioners, many of whom they have known since childhood.
Mr Scott, who will retain his role at McClure Naismith, said: "Jane and I see great possibilities with and for David, who is currently the MD, as the [company] moves forward. We will very much needing David's assistance in terms of, especially in my case, learning about the business. We see David as a really key person. He is a superb guy and we have huge confidence in him."
Outgoing chairman Billy Laing, who steps down on August 1, having joined the company in 1961, said: "We are in a very strong financial position and the company is ready to grow and enter new markets in the south of Scotland and the north of England, which is one of the many plans which the new generation, in the form of Jane and Stephen, have in mind."
Mr Young said: "I have enjoyed working with Jane over the past few years and, with Stephen joining the company, and the skills which he brings, I look forward to the company continuing to flourish and grow under the next generation."