I've been in a similar situation (Been the one with cerebal palsy and accused of being clingy.) The thing that wound me up when my mate dumped me was that I hadn't really been clingy, I was only doing it because she wanted to go off with one of the girls that was bullying me. Just don't walk off, you'll have to give her an explanation first, as just being thrown like a piece of rubbish makes you feel really small. Tell her you need to have time for other friends, but don't abandon her every break. Also, don't be around this girl with the other mates - it made me feel like others were better than me because they were 'normal.' I wouldn't say I was being bullied if I had one piece of bread thrown at me, but the more it happens the more victimised you feel, so it might not be entirely her being clingy. I'll admit I was a bit clingy back then, but I had a real shortage of friends and just felt as if people were really judgmental, so it just depends on the personal circumstances of this girl. I have a pastoral support worker and they can't really do that much - all they do is tell the staff at the school if you give them cause for concern, then the staff handle it from there.