She reports directly to Obumbles, because it's a Cabinet-level position (under Democrap administrations):
http://en.wikipedia.org/wiki/United_States_Ambassador_to_the_United_Nations
Cabinet status
The Ambassador to the United Nations is not a member of the United States Cabinet, but the position is frequently accorded cabinet-level rank. It held this status through the Ford, Carter, and Reagan administrations but was removed from cabinet rank by George H.W. Bush, who had previously held the position himself. It was restored under the Clinton administration. It was not a cabinet-level position under the George W. Bush administration (from 2001 to 2009), but was once again elevated under the Obama administration. Former U.N. Ambassador John R. Bolton has publicly opposed the granting of cabinet-level status to the office, stating "One, it overstates the role and importance the U.N. should have in U.S. foreign policy, second, you shouldn't have two secretaries in the same department."
Whoops, Obumbles is responsible! Nice save for yourself, Hillary!