V.S.
Hi R.,
I know how you feel. Sometimes when kids are hurtful to our kid, it is worse on us than it is on them. I'm wondering if the boy called your daughter a "kid" negative name or an "adult" negative name.
If it was a kid insult, then I think you handled it very well, letting the child know on the spot that he did something that was unacceptable. If he called her by a more adult insult, your speaking to him was still appropriate, but I think you should also take it up with the teacher immediately, and let them know you expect them to handle it with the child's parents.
Kids at that age will assert their dominance in their own way. "po-po head" is a four-year old favorite and needs to be reacted to in that light. Kids need to learn to stand up for themselves and thicken their skin a little at a time. But insulting another child's body shape, physical imperfections, skin color or religion is far more serious. It comes from bigotry at home, and the school has a responsibility to set limits early.