Therese Coffey has no background in Work and Pensions that this site can see. But Downing Street views her as competent, quick to pick up a brief, and loyal: the last weighs even more than usual in current circumstances. She was a Remainer, so her appointment is an olive branch to the distressed centre-left of the Parliamentary Party. And Boris Johnson will have wanted one woman to replace another.
Oh, and Coffey voted for him in the recent leadership election (her boss at Defrea, where she has been a Minister, was Michael Gove). That will count for much. It must be an out-of-body-type experience to be a Secretary of State in current circumstances, with a general election almost certain to be sooner rather than later. We hope that Coffey hangs on tight and enjoys the ride.