For me, the first thing that comes to mind would be that she would likely have the chance to nominate some pretty conservative judges to the Supreme Court. Roe V. Wade could be overturned pretty quickly.
She'd also have veto power over any bill that comes to her desk, which would give her a pretty strong influence on any legislation that comes to law (assuming the Congress didn't have enough votes to push it through regardless of veto).
The biggest thing would be that she'd be Commander and Chief, and dictate our foreign policy. I don't have confidence in her decisions in that regard.