US diplomat's wife on Thursday narrowly avoided jail in Britain for killing a teenage motorcyclist by driving on the wrong side of the road and then fleeing the country.

Anne Sacoolas was given an eight-month prison sentence suspended for 12 months, during which period she faces jail if she commits another offence.

She did not attend the sentencing hearing in London in person and followed proceedings by video-link.

Harry Dunn, 19, died in August 2019 when his motorbike collided with Sacoolas's car that she was driving on the wrong side of the road near a US airbase in southern England.

She left Britain after the accident and the US government claimed she had immunity from criminal prosecution because she was at the base as a dependent of her husband.

A request for her extradition was denied, turning the case into a high-profile diplomatic spat between London and Washington.

Sacoolas was originally charged with causing death by dangerous driving but pleaded guilty to a lesser charge of careless driving which carries a maximum jail term of five years.

Sacoolas had declined to attend court in person on the advice of the US government, her employer, which claimed her presence could "place significant US interests at risk".

"I'm deeply sorry for the pain I've caused," she said in a statement read by her lawyer ahead of the sentencing at the Old Bailey court in central London.

- 'Job done' -
 

Judge Bobbie Cheema-Grubb told Sacoolas that her behaviour "was not far short of deliberately dangerous driving" and passed the threshold for a custodial sentence.

"You drove along the wrong side of the road for much more than a moment and you did not realise what you were doing even when you were approaching a bend," she told her.

But the judge cited mitigating factors including the fact that Sacoolas is the mother of young children "who would suffer disproportionate harm" if she were imprisoned.

She had also pleaded guilty and shown "genuine remorse".

Outside court, Dunn's mother Charlotte Charles, who has mounted a three-year campaign to get Sacoolas to be held accountable, hailed the sentence as "job done".

"Anne Sacoolas has a criminal record for the rest of her life -- that was something she never thought she would see, the US government never thought it would see."

Since the accident, Dunn's parents had been leading a high-profile fight to achieve justice for their son while US authorities stonewalled requests for extradition.

The judge praised Dunn's parents' "calm and dignified persistence" in pushing for justice since the crash, saying they had gone through "three years of heartbreak and effort".

Foreign minister James Cleverly said he hoped the sentence "provides some closure" to the family.