What should I do about my daughter's mean and narcissistic behavior?

My daughter is 15 and she's basically a sweet well behaved girl at home and does well in school. She is especially close to her mother who has spoiled her and always tells her that she's prettier and better than other girls. My daughter has high self esteem and confidence and she is very pretty and very popular at school. But she has been accused of being mean and stuck up towards other girls who have weight problems and maybe aren't as popular as she is. One girl's parents contacted my wife and I and told us that my daughter has been acting very cruel to their daughter and calling her very mean names and that their daughter is very hurt. What should I do to change my daughter's behavior? I don't want to damage her own self esteem but I don't want to see her getting in trouble for thinking she's so much better than other people.