Michelle has known the Bidens ever since she worked as a part-time good-will sports envoy in the Obama administration. Here she is with Joe Biden in a 2008 picture, I think from Boise, Idaho, officiating at a Special Olympics event. (Don't be misled by the date on the caption.

)
Though far from a "career diplomat," Michelle has had some interesting experiences in the political arena. She got her start as a protoge of Condoleeza Rice, Secretary of State for George W. Bush (although, I think Bush was actually morte of a Sasha Cohen fan.

) She learned a lot abput grass roots campaigning when her then-husband ran (insucesfully) for governor of Rhode Island, and she was very visible and active on behalf of the candidacy of Hillary Clinton in 2016.
This is cool. I agrere with poster
@Near above that this is not the most challenging of assignments. (It is possible, though, that some issues of immigration from countries in that area into the U.S. will have to be attended to.) At least English is the official language, although most Belizians also speak some form of native Creole mixed with Spanish, I believe.
Anyway, very cool news. Go, Michelle!