1) there will always be mean boys or girls at school no matter what age
2) You teach your child, how to have her own self-identity and self-reliance. And to know right and wrong.
3) You teach her how to TELL the Teacher, if something wrong is going on or something mean.
4) You tell the Teacher if this is a problem. But some kids just have icky, personalities.
5) At my kids' school, the Teacher routinely talks to the entire class, about behavior and bullying and what to do about it.
6) You teach your child how to speak up.
7) You teach your child about people. How to discern... people. And since she is very young, you teach your child how YOU can help too.
Kids this age, do not have total ability to handle, social situations or people. So YES, YOU AS THE PARENT, need to teach your child and/or talk to the Teacher when a problem occurs.
AND if this Sadie, is routinely causing problems via her meanness... then TELL the Teacher.
Teachers, need.... to know. Or they may not know. So TELL the teacher.
And also since, this Sadie girl is causing trouble. Literally.
So what if kids make drama. IF a kid is picking on your kid or others, I tell the Teacher.
If not, don't expect anything to happen or be corrected.
And a 5 year old, does not have adult skills of deductive reasoning or analysis of behavior.