Libya was the first time a US president imperially waged war without a shred of approval from the congress. It was an unlawful act. The government's role in that should have been hands off. The merits of that war never come into the question; it was not a constitutionally authorized one. Rice is wrong to take the position the president was too passive. He was instead too active, by far.
Congress is unlikely to authorize military intervention in Syria, and so the same point applies there. From a practical view, the US can do little about it anyway. Direct intervention would bring confrontation with Iran. Libya showed that NATO is a paper tiger without the collective muscle to finish off a lightly armed, third-rate regime in the promised days rather than the actual months it took, and we have no reason to believe it would do any better in Syria, and we have every reason to believe it would meet disaster should it pick a war with the Iranians.
The underlying reason the US will not go to war over Syria, though, is oil. The Syrians do not have enough. The humanitarian arguments are cover; Libya was turning to the Chinese for support and trade, the Europeans were alarmed by that, and warmaking by the French, the British, and the Obama administration was the response. That issue is not on the table in Syria. The western powers will not attack because they do not have enough at stake to make it worthwhile.
Rice's remarks were political, not realistic. That is hardly surprising. Conventions are political theater, not forums for serious policy discussion.
Obama's foreign policy stinks. It is the worst of any president in almost a hundred years, damaging to US interests, harmful to the US economy, bumbling and naive, stupidly ideologic and misguided. Rice's criticisms of it, though, are not on target. They should be taken as campaign rhetoric.