Harry Dunn's alleged killer Anne Sacoolas drove on the "wrong side of the road for 20 seconds" before the fatal crash, her lawyers said.
But she was "otherwise driving cautiously and below the speed limit", her legal representatives added.
They have issued a statement detailing the 43-year-old's side of the story.
The American was charged with causing death by dangerous driving after a crash in August 2019 which resulted in 19-year-old Mr Dunn's death.
Mrs Sacoolas claimed diplomatic immunity following the collision outside RAF Croughton in Northamptonshire.
She was able to return to her home country, sparking controversy.
According to her lawyers, Ms Sacoolas "instinctively" began driving on the right-hand side, and could not see Mr Dunn due to "the crest of a small hill".
In a public statement, they said: "Anne did everything she could to assist Harry. After the accident, she ran from her car and tried to help him.
"Anne then saw another motorist approach and flagged her down for more support.
"The other motorist immediately called for the emergency services and Anne made calls to alert the police from the nearby air force base.
"The base police arrived quickly and assisted Harry.
"Tragically, it took over 40 minutes for the ambulance to arrive and nearly two hours passed before Harry was admitted to the hospital.
"Anne did not leave the scene until she was instructed to do so by the UK authorities."
Mrs Sacoolas's legal representatives also made an on-the-record statement regarding her position on the prospect of a virtual trial.
They said: "We have been and remain willing to discuss a resolution, including the possibility of virtual proceedings, with the UK authorities."
'The right thing'
Reacting to the suspect's statement and speaking on behalf of Mr Dunn's family, their spokesman Radd Seiger said: "The parents have noted the statement issued this evening on behalf of Mrs Sacoolas.
"Their position is that these issues should not be aired in any form other than a court of law.
"Once again, they invite her to do the right thing and return to the UK to answer to the charges laid against her."
Mr Dunn's alleged killer returned to the US on a commercial flight after the US Embassy "informed the Foreign Office of this decision and instructed Anne to return home".
Mrs Sacoolas was charged in December but an extradition request submitted by the Home Office was refused in January.
The US State Department has since said the decision to reject the request was "final".