she's probably the best (pre-Reagan) Republican candidate that is possible, since the Dixiecrats have taken over the Republican party.
You put your finger right on it, there. They have - and the Republican base knows it. You remember the Tea Party movement some years back? Most of those reps/senators found themselves marginalized and shut out of important positions by the "establishment party" in short order. This election has seen the issue come to a head - Trump is universally loathed by the party's "old guard" and the guy who emerged as a front-runner against him was - you guessed it - a Tea Party Senator. Incidentally, Ted Cruz was and is loathed by his Congressional colleagues for his constant grand-standing and stunts on the Senate floor, much of which seems to have been done simply to build his reputation as "tough" or something - almost like he was planning to run for President all along. Thus the party's Old Boy Club had to back Cruz - a man they hated - because they hated Trump even more!
What's really telling is how Cruz was talking in the later days of the primary campaign - he actually called Trump voters "low information" and later said of Trump (after Trump had won a few important states in the primaries) that it was "time for the clowns and dancing bears" to clear out of the circus. Up until that first vote, it was possible to shrug Trump off as a demagogue who people considered entertaining, but not a serious option for President. After it, he was a real threat - because he'd received the actual votes of the people. And yet, right up to the last days of the election campaign, Cruz - and the old-guard party who'd swallowed their disgust to back him - consistently insulted the very voters they needed to back them up. They seemingly had no cognizance of a democratic system being one where the voters choice is the final arbiter of power. This is always the ultimate failure - for an excellent example, compare the backlash from Hillary's "Deplorables" comment to the similar backlash Romney received when he issued a similar insult to the other side's voters. In both cases they were talking about people who weren't going to vote for them anyway, to their own supporters - but it still impacted them negatively, because it's never a good idea to insult voters. People that would've stayed home on election day will go out and vote for your opponent just because you called them names - and they resent it.
The Republican party hasn't been representative of most Republicans for a while now, as you point out - and on top of that, they've insulted voters who think they ought to be. Even more interesting is how well Bernie Sanders did - a Ralph Nader tier candidate came within ten points of toppling and Old Party powerhouse. Like you say, she's much like a more liberal pre-Reagan Republican in many aspects, and her party knows it, which is why they flocked to the much more liberal Bernie.