Haley's sentimental feelings

One of Haley's friend repeatedly told her that "You are not my friend!" in several occasions. Haley is a very sensitive little girl, she comes to me and tells me that her friend doesn't want to play with her. I explained to her that sometimes her friend may want to play alone or play with other friends. She picked up this line and she told Chester that he is not her friend. I again tried to explain to her only mean girl will say this, and we want to be nice girl instead. Seeing the facial expression of disappointment and sadness on her face hurts me. I wish my girl doesn't have to hear these verbal abuse, but I guess this is part of growing up. What can I do to better ease her sentimental feelings!??