The Rezko trial is wrapping up. I think The Clinton's are waiting for that. If he's found guilty, and they hand a buttload of years on him, he may start talking.
And he may start talking about O'bama.
Another reason is she is positioning herself to run against Mc Cain in 2012. I think the party leaders think O'bama can win because they are locked into the party line.
Either way, it's her right to stay in and wrangel concessions. If she's VP, Bill will have him off'ed. It's a win-win for her.