"My friend was recently sexually assaulted and she beats herself up for not fighting back. And to be honest I don't really understand why she didn't, what am I missing?" Confused
I can understand why your friend is distressed, and I can also understand why you're struggling to understand her actions. But it's also completely expected.
Sexual assault, whether it be unwanted grabbing and touching, all the way through to rape is (to state the obvious) highly distressing. And people respond to distress and trauma in fairly predictable ways. Most people have likely heard of the "fight or flight" response, but there is one more very important "F" that keeps getting left out:
Freeze.
It's important because it's actually incredibly common. And we all do it, if we're put under enough stress. You've likely encountered stage fright, felt like a "deer in the headlights", or found yourself momentarily lost for words.