It is the rejection that hurts but you have to accept it & move on like she has
Deal with it. Either hide in your room or go out and be social somewhere else.
You can go out without having a destination..if you are that uncomfortable......I mean go for a walk and get away from her
If you do happen to see her, just act really happy like your life is amazing. It will give off the impression that you are completely over her and things won't be awkward