Hail to the Chief

We have a new president. Frets about her "militancy" should be ignored - as the president is to complete the previous chief's term, which ends in December, she won't be making changes to the executive.

Though why her term should be so abridged, I can't say. She was already vice-president, why did she have to be elected again, merely to complete the previous president's term? I suppose she has somewhat more "authority" now, but why not give her a full term in office? I may be obtuse, will someone please explain the logic at work here?