Because she, not being a "gun person" and certainly unarmed was probably shocked and more than a little scared. She was scared anything else she did might just set him off.
If I were a female, non-gun person, by myself, and a person of that stature were to start a threat like that, I wouldn't merely turn around. I would have freaked out screaming. Bad move? Yes, it may have been. As you stated, it might have escalated the issue.
But, IMO, it's even worse to think that one would just turn around from what might have been a bullet to the back of the head...or worse.
I wasn't there. I don't know the whole setup. But, to post an extremely vague post in a Tactics and Training forum and not question the content does no good for clearer suggestions.