Unfortunately, those stories are all too common in customer service. Instances of being acted upon are rare and, at worst, you're more likely to get a notice from corporate headquarters, based on how they perceive the situation. So if nothing else, as frightening as it was, you'll probably be alright even if she comes back. Though I hope she doesn't, that shit's scarring. 

I can only remember one real genuinely angry death threat. Reacted about the same as you - teared up and freaked out - with a few differences aside.