Sacoolas, 43, was allegedly driving on the wrong side of the road when she hit 19-year-old Harry's motorbike in Northamptonshire on Aug. 27.
She claimed diplomatic immunity after the incident and returned to the U.S. on Sept. 15, sparking an international outcry.
Sacoolas was charged in December with causing Harry's death by dangerous driving.
Despite the U.K. making an extradition request for Sacoolas, Prime Minister Boris Johnson said the chances of her returning were "very low."
The State Department said the request for Sacoolas's return was highly inappropriate and would be an abuse.
Now, Secretary of State Mike Pompeo has rejected the extradition request, family spokesman Radd Seiger revealed.