H.D.
Is she on any prescription medications? Nightmares may be a side effect. Is she getting bullied at school or on-line (my space, facebook...)? I would say she is not faking it if she is writhing around in her sleep. Since this has been going on for so long I would consult the doctor if these can't be explained by meds or bullying. If she is on meds I would ask the doctor to change the meds and see what happens. There are no studies of medications on children (only adults) and side effects can be different for children. good luck!