In the '92 presidential campaign, the Clintons openly disclosed their use of private detectives to dig up ammunition on women who had accused the presidential candidate of having affairs with them, disclosing that they paid detective Richard Palladino over $100,000 in campaign funds. But, of late, they avoid such embarrassing disclosures by hiding their detective bills in their legal expenses.
The likeliest theme of the Clinton attack will be Obama's inexperience. They'll seek to portray him as naive and way over his head in a world of terrorists and threats. But the risk here is that a woman is normally seen as weakest in the military/national security arena, so Hillary might find it difficult to make the issue work for her.
A better choice might be to argue that her political experience (i.e. in defeating the GOP "attack machine") makes her the better candidate for the November election. With the Democrats anxious for victory, using Obama's politeness and gentility against him could be an effective strategy.
She would, in effect, suggest that he is too nice to beat the Republicans - an accusation she can be confident nobody will ever make about her.