Hi TD - my DD had some problems at her last school, started with difficulty making friends and grew into a full-blown harrassment scenario.

These are the things that we did that helped:
* Booked regular meetings with class teacher - asked her to instigate a buddy-system within the class and tweak seating arrangements
* Booked meeting with vice-principle - she held a round meeting with the class to iron out the harrassment problem & also gave a chance for other chn to voice the problems they were having with my DD (ie she was unwittingly annoying her classmates by singing to herself during work time LOL and needed to be made aware of the ways she was p*ssing them off).
* Joined Guides Australia - this was the single most important thing we did - it gave DD a community of supportive peers and nourished her socially when things were off at school. You could try a group like scouts or a church-based group depending on what is available locally
* Ultimately though, what helped the most was a move to a new school. This coincided with an interstate move but had we stayed there we would've given it serious consideration. Now DD is in a catholic school and she says the students are much kinder and more considerate generally - plus a lot of things that were social issues at the old school (what clothes, phone, games, etc you have) are not an issue here because of the strict school rules. Something to think about anyway.

Good luck, there is no simple solution - you will have to keep vigilant and keep raising it until it is resolved and then keep an eye on it anyway.