My younger son (2.8) sounds very much like your daughter. He is not in preschool yet, he is home with me and is very withdrawn from social situations. And for about 4 months got to being aggressive and wouldn't tolerate any children near him. He does get services from early intervention and will be getting evaluation for autism but even his therapists aren't quite convinced whether his issues are autism, high IQ or both. Either way, even with the aggression issues, the school itself is already recommending we put him IN the special ed public preschool that my older one just started. ... there are mainly kids with speech issues but some other as well. But the special ed department is strongly advocating putting kids like my son into the normal setting and if he needed a one on one aide, they would most likely provide that to get him the services he needs.

now, to give you some hope, we have just recently in the last 2 weeks seen the aggression completely disappear! He is still disinterested in socializing but no longer cares about anyone entering his space. I believe it's due to serious dietary changes we made 4 weeks ago ... but it could also be caused by something else ... some chemical changes of sorts? ... it started in June and not it's all gone.

so, my point is ... I would NOT let the school label my child and place in a setting where things could get possibly even worse! And I would also try to look at what may be causing all this?