I have seen several possible reasons advanced for the objections to Susan Rice becoming Secretary of State. There have been accusations that people object to her race or gender. I think it is far more simple than that.
Five days after the attack that killed the Libyan ambassador, she went on a series of talk shows and told a bald face lie - that the attack grew out of a protest over a YouTube video and had nothing to do with terrorists.
I am sure that there is a lingering suspicion that Obama would have lost the election if the electorate knew that al Qaeda, an organization that President Obama claimed was no longer a threat, had mounted an attack that killed an ambassador. Rice gave political cover for her boss during a tight election and the Republicans can't forgive her for it.