If she starts out as really rude you should say "Ma'am, I'm more than willingly to help you do your job but I require you to be professional with me and lose your attitude. I am a customer and I should be treated with respect since as of now I have done nothing wrong" and she'd probably straighten up and apologize on top of it...
Sometimes someone's having a bad day and just doesn't realize it's coming through in their tone and demeanor.
Sometimes someone's having a bad day and just doesn't realize it's coming through in their tone and demeanor.