I don't think Valerie thinks she has the slightest chance of winning the nomination for herself so she could push Michelle to act as her front person.
Even if Michelle made all the POTUS decisions (and I don’t doubt that) she has no RESUME. Her only real job was for $250K/yr. to chase uninsured patients away from a Chicago hospital. Does she want to run on THAT?
Or does she want to claim she was actually POTUS and expose the Kenyan as a sock puppet?