Why do people with eating disorders often accept an invitation, but then not show up?
Most people think that if you have promised to meet someone you should come whether you want to or not. To stand for your word. That is a responsible and considerate attitude.
However, a person with an eating disorder may be so depressed after a day's eating and vomiting that she doesn't want anybody to see her. When she agreed to meet you, she thought she could manage it, but then her day went off the track and she was caught in her eating disorder.