My theory:
Women were told for years that in order to progress in this "man's world", they have to reject all the traditional elements of womanhood - beauty, motherhood, soft wisdom, social grace, etc. Bras were burned, makeup was discarded, and marriages were broken in order to "liberate" women. Sure, the price was high, but entire worldviews were invented to justify their decisions, and small gains were trumpeted as major victories.
Not every woman agreed with it. Some definitely became True Believers. Others strongly disagreed with The New Truth. And some, possibly unaware of the forces moving around them, secretly wanted it to be so, but weren't willing to burn their bras and leave their families.
Enter stage right: A good looking woman who stands by her family. Who succeeded in "this man's world" by not trying to be a man. Who rejects all of the revolutionary bits of the feminist dogma. And who proves that you don't have to reject the feminine to be a feminist.
Suddenly, all of those True Believers are faced with someone who, if she's right, proves that everything they believe in is wrong. Even the bystanders see that their quiet rooting for "the home team" wasn't as justifiable as they thought. They have to tear her down, or realize that their identity is a fraud.
OTOH, Sarah is getting canonized by the conservatives. And this worries me. We should not idolize our politicians; they're very human. The Left traditionally engages in hero-worship, turning their idols into philosopher-kings. And we all know how most of them died... at the hands of angry mobs.