How do you deal?

I have a social obligation this week which promises to bring me in contact with an associate who, the last time I encountered her , was UNSPEAKABLY rude.  I would like to ( quoting Jacqueline Kennedy) cut her dead, but I was not raised that way.  My mother gave me constant lessons in manners and social etiquette is ingrained in me.  I hope I can just avoid this person. The problem is, she sees nothing wrong in her behavior and she has a HUGE ego about her abilities ( my mother would have said "well, SOMEONE has to like her" see Mom COULD be snarky!) I hope to avoid her.  Fingers and toes crossed, but it does make me wonder, how do you deal with interacting with people you would not be friendly with if you were given the choice? One thing is for sure, I will keep my mouth closed and move away if I am near this person.  Not a fan.  Funny because before I got to know her, I liked her.