If they are serious about Michele they better hurry up and get her on some primary ballots and debate stages - and she better win SOMETHING.
The DNC is certainly not above using super-delegates to rig their primaries, but even Democrats need to have some process that vaguely resembles a democratic selection.
They can’t just magically announce Joe is out and Big Mike is the nominee.
There is an unqualified black female that COULD magically become the nominee though - Kamala Harris - and it would even be Constitutional:
Biden steps down for health reasons. Harris is now the first black female POTUS. And now she’s running as incumbent.
Yes they can. They do whatever they want with impunity.