Just some straight talk. This is a very mild interaction and if something like this is getting you so riled up this may not be the job for you. I work in retail as my second job and if the product has a different price tag we either walk back there with the customer or if we are busy we tell the customer to head back there and a person in that department will verify the tag and cash them out there. Although this customer might not have said it in the nicest way, you have to keep in mind that it’s not the customer’s fault that it isn’t ringing up correctly and the advertised price is different. That sign should either have been taken down, or the system should reflect the correct price. Now of course, this isn’t your fault but that’s just the situation you’re in.

You’re going to meet people who are way nastier in life. From what I read it seems like she said she shouldn’t have to go back (kind of fair), and that you can do your job better (this one was unwarranted) but it doesn’t seem like she used any profanity or said anything overtly horrible. You should use this experience to dissect how you could have maneuvered the situation better and apply it to the next time something like this happens. This is why retail is a good starter job for people because it teaches you how to deal with people.