Agree with @ChopperC110P - I was bullied at school via ostracism, and it took me months to realise that was what was happening - I seemed to make a friend, and then they'd just be 'unavailable', so I'd make another friend, and the same thing would happen, so I'd think it was me and feel absolutely worthless. In reality this one particular girl was pushing/manipulating them against me. All the time there was nothing obvious for me to complain about - no name calling, no bitching, teasing etc, it was just this gradually building wall of silence, as more and more girls were pulled into it against me. They'd speak to me if they had to (eg under the eyes of a teacher), but otherwise they'd avoid me.
Evrntually I confronted a girl who'd been my friend, and she admitted that she'd decided not to speak to me aftera conversation with the main bully, and suddenly I realised what had happened, and went to the teachers, who intervened, and managed to put things back on an even keel, but I didn't stay in touch with any of the pupils from that school as the damage had been done.
I just wasn't very good at political/social sensibilities at that age and it left me vulnerable to horrible treatment like that - not been diagnosed as nd, but I do have a lot of traits fond in people who are nd.
So definitely consider if this might be the case with your daughter. Don't just chalk it up to random 'bitchy girls', as it could be far more sinister.