Friends that are unwilling to understand

I had a best friend that I had known for 13 years I have been in special ed for 8 years because I have Social Anxiety, General Anxiety, ADD and a Learning Disability in writing/reading and math. I told her everything and she did the same. In 9th grade she started using the R-word and every time we would get in a fight and have to stop in the frame of mind that you are just not ready to learn and change your way of thinking. One day we were eating lunch just her and me and one of her friends. Her friend put and orange peel in her mouth and smiled. So my friend asked “can you do that again?” so she did she then said “That’s so special Ed”. I told thats not ok to say and it offended me and she had the audacity to say “well, its not directed towards you” well you know what it is and I left and she hasn’t talked to me scene. All I wanted from her was just to have enough respect for me to just try not to use the R-word. The worst part is that she knew how I felt and said it any ways.