The suspect in the crash which killed Harry Dunn is “wanted internationally” after an Interpol notice.
Mr Dunn 19, died after a crash in Northamptonshire in August and US national Anne Sacoolas is suspected of causing his death by dangerous driving.
A Home Office extradition request was rejected by the US in January.
In an email from police to Mr Dunn’s parents the force said “the wanted circulations should be enacted” should Mrs Sacoolas leave the US.
Motorcyclist Mr Dunn died in a crash with a car near US military base RAF Croughton on 27 August.
Mrs Sacoolas, the wife of a US intelligence official, claimed diplomatic immunity and returned home.