Most students would feel a £20,000-plus fine for driving over the limit was a calamity, but Katharina G Andresen got off lightly.

Andresen, 22, was handed a NOK250,000 (£23,000) fine by an Oslo court this week after she failed a roadside breathalyser test while on her way to the family chalet in the ski resort of Hafjell, three hours north of the capital, for the Easter weekend.

Drink-driving penalties in Norway are means-tested, and since Andresen – a tobacco heiress with assets estimated at NOK7.7bn (£710m) – is reportedly the country’s richest woman, the fine could have been much higher.

“If the decision in this case was based on a normal return on the accused’s assets, the fine should have been set at NOK35-40m (£3.2-3.7m),” the court said in its judgment, according to the newspaper VG.

Andresen, who was found to have a blood alcohol level of 0.06 – three times over the legal limit, which at 0.02 is one of Europe’s strictest – more than an hour after she was stopped, successfully pleaded that she had limited means. The equivalent in England, Wales and Northern Ireland is 0.08 and many Europeans have a limit of between 0.04 and 0.05.

While the state prosecutor demanded the stiffest possible penalty and 18 days in prison, the court accepted that she had “no fixed income” and “the assets she possesses, at the date of this judgment, have not yet yielded a dividend”.

In normal cases, Norwegian judges fine drunk drivers 1.5 times their gross monthly salary, but they have discretion to increase the amount based on what they consider to be the “real financial position” of the defendant, VG said.

Andresen, who was also banned from driving for 13 months and handed a suspended three-week prison sentence, said she regretted her error of judgment. “I thought I had waited long enough not to be over the limit any more,” she told financial daily Finansavisen. “I am very sorry.”

The heiress was given a 42% share in her family’s investment firm in 2007 and is ranked the world’s second-youngest billionaire by Forbes magazine. The family’s wealth stems originally from its acquisition of the celebrated Norwegian tobacco company JL Tiedemanns Tobaksfabrik in 1859.

• This article was amended on 17 November 2017. An earlier version said that the UK blood alcohol level limit was 0.08. This is the limit in England, Wales and Northern Ireland. The limit in Scotland is different to the rest of the UK: 0.05.