Doctor's Office Karen

So I currently work as a medical assistant (not saying where for privacy reasons). Today, a lot of patients were canceling their appointments due to the bad weather. There was a lady (the Karen of the story) and her appointment was at the end of the day. I called her to see if she wanted to move up her appointment to an earlier time because there were lots of gaps in the schedule. I called her, and, initially, she said that she needed to keep her appointment because that was the only time that would work for her. Later today, she called us to change her appointment to the spot I was trying to put her in. She tells one of my coworkers who answered her call that she just got out of work and that she can make it by 3 pm. Her appointment was initially at 4 pm. This is where it gets bad. A little while after she changed her appointment over the phone, she called us back enraged. She called another one of my coworkers who answered her call and told her that she wouldn't be able to make it at 3 pm, and she's coming at 4 pm instead. She was mad that her appointment time was changed and that she couldn't make the time that she changed it to??? Makes absolutely no sense. Then Karen tells my coworker to "go to hell" because she "wasn't doing her job", and that no one in our office has our shit together. Then my coworker told her, "You can take this up with my manager if you want". At that point, she transferred her to the manager and hung up. I can't believe how rude Karen was to her. Then, she came to the appointment, and she was kind of b*tchy to the front desk lady. However, she was able to calm Karen down which was good. I then grabbed her from the waiting room, took her to the exam room, and did her vitals, etc. She was nice to me which shocked me, to be completely honest. After that, I didn't have to encounter her for the rest of her office visit. In conclusion, this was a tale about the consequences of your actions. Hopefully, she doesn't yell at us again. Yikes!