This person being mentally handicapped has nothing to do with your post, unless you are feeling embarrassed about what happened. The story could read as follows:
"I went to Easton to see a movie. I ran up the incorrect escalator, and the person taking my ticket did not approve. She let me know as much, and we went on our way."
I don't see what she did wrong. A mentally handicapped person contributing to society, earning a paycheck (could be supporting herself rather than on government subsidies), and someone is complaining about it? Come on now, look at it differently, admit that you were wrong, and that's that.