I think Americans may have had enough of "minority candidates" for a while (a black man and then a female??). Our own choices have been entirely mainstream since Maggie was defenestrated.
That said, it's a matter of who she'd be up against. Normally, the opposition candidates would be fairly clear by now, but the Republicans still seem to be tearing themselves apart, middle-of-the-road v Tea Party. If she'd faced Mitt Romney she'd have beaten him too.
The Democrats themselves don't seem to have produced a more promising candidate than Hillary yet, so she'd be in with a very good chance of getting the nomination at least.