She perhaps sees this as a way to build some credibility on foreign policy and get good regular exposure on the news.
She'll be seen not as fighting and arguing (as she would if she stayed in the Senate), but consistently trying to bring people together and solve problems as the nation's top diplomat.
On the surface, this looks like a gesture of conciliation and inclusion designed to heal wounds and help the nation.
On the other hand, Obama has expressed admiration of Abraham Lincoln's way of bringing his former adversaries into his Cabinet.
But Lincoln's move actually neutralized his enemies by disconnecting them from their power bases and making him their boss.
Hillary's Senate confirmation hearings would finally bring to light the previously hidden sources and methods of funding for Bill Clinton's foundation.
What's uncovered by the Senate could be very embarrassing for her, even to the point of torpedoing her nomination.
I think Hillary sees this, as risky as it is, as a better path toward the Democratic nomination, be it in 2012 or 2016.
I think Obama sees this as a way to make his re-election bid easier in three ways:
It's a nice political gesture.
Since Hillary will work very hard to prove herself worthy, she will either prove him right or hurt her reputation if she fails.
Plus, he's keeping in mind the old saying, "Keep your friends close and your enemies even closer".