LONDON — An American woman who fled Britain after her car collided with a teenage motorcyclist in central England in August while she was driving on the wrong side of the road has been charged with causing death by dangerous driving, British prosecutors said on Friday.

The woman, Anne Sacoolas, the wife of an American diplomat, left for the United States under diplomatic immunity three weeks after the crash, enraging the family of the teenager, Harry Dunn, 19, and starting a diplomatic tug of war as British officials urged her to return.

The British Crown Prosecution Service said on Friday that it had started proceedings but that it was up to the Home Office to decide whether to formally seek Ms. Sacoolas’s extradition through diplomatic channels.

[Update: U.S. refuses extradition in fatal crash, prompting anger in the U.K.]

There were no signs, though, that the United States would send Ms. Sacoolas back to Britain. During a meeting between Mr. Dunn’s family and President Trump in the White House in October, Robert C. O’Brien, Mr. Trump’s national security adviser, said there were no circumstances under which Ms. Sacoolas would return to Britain, a lawyer for Mr. Dunn’s family has said.