Yikes! What a cow. But as colorbook said, she's likely an unhappy soul and one who wants to make those around her as miserable as she is!
I've worked in retail but if I'd had a customer that rude, it's been erased from my memory. I do, however, recall dealing with someone when I worked as a lab assistant/phlebotomist. I was the only person working the evening shift at a collection site and I had just locked up for the night. I get this guy banging away at the window. Since he saw me seeing him, I figured it was best to find out what his dilemma was. I opened the door and politely informed him that we were closed for the evening. His response, "I thought you were open until 8 p.m." My response, "yes we are but it is just after 8 p.m. now." Him, "not by my watch." Me thinking but not saying "oh the world revolves around YOUR watch." It became painfully obvious this guy was going to stand there and rant and rave, so I decided to have him come in and take his blood. I proceeded to be as polite and accommodating as I could possibly be. During the process he gives me his "I'm having a lousy day" explanation and apologizes. I felt like saying "yeah thanks to you I'm having a lousy day too!" but I wisely keep my mouth shut and just say "no problem" and usher him out as quick as I can. The one bit of satisfaction I got from that episode was the fact he left feeling like a dick.
I understand people can behave like assholes when they've had a lousy day or experience. I hate to admit it, but I've done it myself. (Just once. As a REALLY offensive b*tch. When this kid in one of those big chains was trying to give a sales pitch about purchasing the store warranty. I had been ripped off by this store when I purchased a warranty, so I wasn't about to let my Dad, who I was with, get suckered into wasting his money on it. Ah, but I digress.) So in that respect you can kind of feel for the other person. But when someone else puts you on the defensive, it isn't so easy to sympathize. In the end I've found it easier to paste that plastic smile on your face, be as pleasant as you can muster, and whisk that person out of your life as quickly as you can. A friend of mine got too good at it though and now has to deal with the local pain in the ass every time he goes into her store.
Anyhow, the good news for you is that you likely never have to see that woman again!