How do I teach my 3 year old that she should not bite other kids in school?

You can tell her biting is wrong and we use teeth to bite food instead of biting people. Keep repeating and reminding of the wrong behaviour. You can borrow this book titled teeth are not for biting so your daugther can relate the situation better. If she only bites in school, try to check with teacher under what situation she bites? You can teach her anger management eg. Inform teacher if there is any bully in school. 3 years old is able to comphrehend well.