At my daughters old school there was a child with a nut allergy. All the children were made aware of this and had it explained to them the seriousness of this condition and what to do if an allergic reaction should occur. They were all told that ifthey had food which they knew had nut traces in it, to sit at another table to this child at meal times. They were educated in the importance of washing their hands after handling food. My daughter became very aware of what foods had nuts or nut traces in them. My daughter now not only has a knowledge of how important it is that a person allergic to nuts has NO contact with them and an awareness how important it is to get help IMMEDIATELY should an allergic reaction occur. She knows what an epipen is and how one should be used. Consequently she goes out into the big wide world with the knowledge that could one day save someones life and at the same time the child who had the allergy goes out into the big wide world having led a nearer normal school life and with an awareness of how to fit into everyday situations without being wrapped in cotton wool. Sometimes we have to compromie and find a half way point. Parents with autistic children know this only too well! (I am one myself) It may be worth investigating if there is a child with a nut allergy at your childs school - or indeed any other allergy - and asking what they have done to educate the children about such allergies.
It appears to me that the school also need educating on how to handle issues with autistic children too. I hope you can persuade your daughter to eat nuts again and that we can all learn to live together in a society where living together means we are aware of each others needs and how to deal with them rather then just sweeping them under a mat by banning them so they cant harm us. I firmly believe education is the way to go here. Banning will just lead to more ignorance - and I do have a sister with a food allergy that has almost killed her three times, she also agrees that banning is NOT the answer. More education is.
Cheers, Lucy