You definitely need more information to address this. What specifically is she saying? Who is she with when this happens? What environment is she in? You need to know this for two reasons: (1) you can’t coach her on what not to say if you don’t know what she’s saying that is considered “mean”, and (2) it could be that she’s being “mean” to be accepted by her peers, or to deflect negative attention away from herself. This ties in to what Tracy said above: you can’t change behavior until you know WHY it’s happening and address the WHY.
I have used if-then social rules with my son. You can structure the same for your daughter. You may need to talk about how derogatory comments don’t make you “cool” or “accepted” even though it often seems so.
I would also get the school guidance counselor involved. Developing healthy social relationships is part of their job. There have been several years where my son worked with the guidance counselor on social struggles and the counselors have always been very helpful.
ADDitude Community Moderator, Parenting ADHD Trainer & Author, Mom to teen w/ ADHD, LDs, and autism