Was the principal or assistant principal involved? If you feel like you can't let it go and you need to take it up a level send them an email detailing the situation. I've had to go over my son's teachers head many times.
Last year a teacher took a misunderstanding and blew it out of proportion and banned my son from computer lab for the rest of the year. I had to take that to the assistant principal and he was able to get it straightened out.
If your daughter is having issues with this boy, make sure to keep track of all the details, and let the principal or her teacher know each time something happens. It's sad that we have to report every little thing but unfortunately if we don't something like this happens and the liars seem to prevail. We had an incident earlier this week where a boy, whom my son was friends with, lied and almost got my son in trouble. Luckily the assistant principal knows my son well and was able to diffuse the situation but he advised me to make sure we report any issue immediately.
It's so frustrating, my son like your daughter gets so upset when some thing is unfair. They do have to learn that not all things in life are fair, but we also need to make sure they know to stick up for themselves and you don't always have to take it or put up with it.