Any parents with older children in here?

I am feeling defeated....

I looked up everything on how to help my daughter deal with "mean girls" and not to become a mean girl herself and how to hold her tongue and just walk away. How do you teach your child that they don't always have to have the last word? And to be the bigger person and just walk away...

I have been dealing with this for years. Even put her in counseling to then be told there is nothing wrong with her....

---i can keep her from her "friends" for right now because its summer but what happens when school starts and I can't always monitor her action?