I would sit DD down privately and tell her all the awesome things about her that you and other people love about her. Discuss how its not nice to do those things to others, and then its not ok for people to do them to her either. Arm her with strategies to avoid those situations (refusing to even take the note from the other girl, taking it and throwing it away without reading it, etc etc) Remind her of what being a friend really means, and remind her of those people who are her real friends. She deserves good friends, not nasty people.

Take this to the teacher and principal too. A stern discussion with the whole class, and school at assembly might also be a great way to empower children to not allow this kind of bullying to occur. A notice in the newsletter is always handy too, as is a poster ont he class doors and in the bus (if thats possible).

Sorry for such a scattered post!