RD, im in a rush right now so will be coming back later to re-visit.
My quickest advice right now, having worked quite extensivley with children affected by Autism of all ages, would be to speak to the teachers and school about this and its negative affect on your daughter AND other children. If the teacher can do a group discussion or just explore this matter more in-depth as a subject with all of the children, barriers and perceptions could be shifted amongst the children themselves. Once this change is in motion, parents and their children will be more knowledgable and therefore comfortable with dealing with any occurences should they happen at a sleepover. My guess, would be that people are under-educated on this condition, it doesn't help that the media paints children with Autism as 'crazy and wild' when they're often highly intelligent! This plan of action will take time, but it is possible for this to be overcome. I believe it.