Harry Dunn’s mother said the family’s “determination was stronger than ever” to bring the woman charged with causing his death back the UK.
The Dunn family met their MP Andrea Leadsom to discuss what the government would do following the US decision to refuse Anne Sacoolas’ extradition.
Mr Dunn, 19, died after a crash on his motorbike outside RAF Croughton in Northamptonshire in August.
Charlotte Charles said: “She has to come back, it’s the right thing to do.”
Speaking after meeting Mrs Leadsom in Towcester, Mrs Charles said: “Our determination is probably stronger now than ever, if that’s possible.
“We very much feel supported by her and the government.”
Harry Dunn’s father Tim Dunn described the meeting with Mrs Leadson as “promising”.
He said: “I feel like she’s behind us, I really do.”
Mrs Sacoolas, the wife of a US intelligence officer who worked at the base, left the country under diplomatic immunity following the crash.
Extradition proceedings were launched earlier this month.
The US Secretary of State Mike Pompeo turned down the extradition request in an email to the UK Government on Thursday evening.
Mrs Leadsom, who is also the Business Secretary, said “it will take some time to consider what the government’s next steps should be” but it was “determined to see justice done for Harry”.
She said: “There is no way that diplomatic immunity was to be used to leave a grieving family behind who are absolutely heartbroken.”
The prime minister’s spokesman earlier said the government would “carefully consider” what future action could be taken and was “urgently considering” options.
He added the Crown Prosecution Service was considering the legal position.
Foreign Secretary Dominic Raab said he had told the US Ambassador the government was “disappointed” about the decision and that the UK “would have acted differently” had the crash occurred in the US and involved a UK diplomat.
“We feel this amounts to a denial of justice and we believe Anne Sacoolas should return to the UK,” he said.