Not necessarily saying it wouldn't have happened if someone else was SoS but could she have done more to prevent the attacks? When you take a look at all the violence in the region months ahead of the 9/11 attack and the journal of the ambassador and the requests for increased security could something more have been done? If they wanted to keep a low profile then why didn't they just pull them out of Benghazi all together?
The US has 294 consulates, embassies, and similar diplomatic compounds around the world. 27 of them are in the Middle East and North Africa. It's not possible nor ideal that the Secretary of State spends all of their attention on micromanaging the security of each and every foreign diplomatic mission. The State Department employs tens of thousands of people, and hundreds are likely assigned to embassy security. If it was possible to prevent the attack, the reason why it didn't happen was because of a systematic issue, not because of the failings of one single person on top.
Hillary Clinton takes responsibility for it because that's what you're supposed to do when you hold a position of authority and people below you make a serious mistake.