Brandy is a bit insecure and a perfectionist. Vocal duress, after doing broadway , I would think that she knows how to protect her voice. I think Brandy is hard on herself and the pressure became too much as the event became bigger and bigger.
As many of us have flown and spent a lot of money, she could at least do a meet up with her fans. She should already be in DC if she was really anticipating performing. And if she is not here and knew days ago she would cancel then shame on her.