It is unfortunate that your daughter has to go through this situation at such a young age. If you find that she cannot handle this on her own, after she has confided in you, then go to the teacher and seek some assistance in the matter.
I have often witnessed the harrassment of people by so called "Christians" for not believing as they do. When I am approached by them, I usually ask them if they are a "Christian" and what are the two greatest commandments that Christ gave to us. They usually answer that there are ten not two commandments. To which I very gleefully reply, sorry you are wrong, Christ came to fulfill the law not replace it, and the two greatest commandments are to Love your God before all else, and the second is to love your neighbor as you love yourself. Obviously you must hate something about yourself, so go clean your own house before you start trying to clean mine. Have a blessed day. I then walk away leaving them sputtering and trying to come up with some clever response.
A possible solution to this problem would be to see about having the school institute some form of diversity awareness program to teach all the students about the different cultures, beliefs, and traditions. And if an objection is raised by some of the parents, then I would remind them that under the US Constitution that all people are granted the right to freedom of worship, and that also all men are created equal, with the right to pursue life, liberty and the pursuit of happiness.
And of course if all else fails, Sue them and the school board for physical, mental and emotional distress to you and your daughter.