I can't believe this thread is still going...
OP, the issue with your belief that we all just need to read our emails more carefully and have more training is that every autistic child is just as unique as any other. All autistic children will have different triggers and different needs and different coping mechanisms. There is no 'one size fits all' approach to teaching children with autism. Getting more training would be great, but theory only takes you so far when you're dealing with real people.
Moreover, the 'plans' we get sent are often as useful as a chocolate teapot - 'Sarah likes to talk about teddy bears and doesn't like to share. Sarah gets anxious when she doesn't understand instructions. Sarah takes everything literally so make sure you don't use euphemisms' would be a typical 'plan' in my experience. All that tells me on a practical level is to be as literal as possible when giving instructions. If this fictional 'Sarah' walked into my classroom for the first time and I had told her I didn't know where she was sitting, there would be nothing in my plan to tell me that this would cause a meltdown.
Learning to get it right with an autistic student takes time, patience, and often trial and error. I am only just now - one whole term in - getting to grips with how to make the classroom a safe space for the severely autistic child in my form group. It's taken me a good three months to work out what works best for him. His 'plan' just tells me he doesn't like electric noises and to allow him to wear ear defenders if he gets overwhelmed. That's it. The rest I've had to figure out for myself. Thankfully his mum is very understanding and supportive and gets that we're all on a journey together to learn how best to help her child manage school, and when something's gone wrong, we chat about it, chalk it up to experience and learn from it rather than her accusing me of being rude or uncaring.
You seem to be unwilling to appreciate that your expectations of your daughter's teachers are a little unreasonable. Expecting a teacher to get it 100% right with your daughter, who by the sounds of it has considerable needs (you don't seem to think so, but in my experience, a child who has such a severe meltdown at school that they need to sleep it off is a child with high needs) in their very first lesson with her is utterly unreasonable. You need to allow the teachers time to get to know her.
You do also need to get over this strange idea you have that in professional settings, everyone is automatically able to switch off their personalities and be polite and kind all the time. For most people, the occasional snappy comment under pressure is going to come out from time to time. It doesn't make them bad people or rude people. It makes them human. Saying there is 'no excuse' for rudeness in a professional setting is idealistic in the extreme. We are not robots. All of us have the experience of being snapped at by someone in a professional setting, and I'm sure all of us have been able to appreciate that it was nothing to do with us and everything to do with the person having a bad day for whatever reason. We've all been there, and so none of us have the right to judge.
Of course you are not unreasonable to be sad about the fact that your child has missed out on something she was looking forward to. It must be incredibly difficult to watch her suffer as a result of her autism. But blaming her missing out on her Christmas lunch on a teacher who spoke to her a little harshly the previous day is unreasonable. It is not the teacher's fault that your daughter had a meltdown. The teacher had no intention of causing your daughter to have a meltdown. Your insistence on wanting to apportion specific blame rather than accepting that school is an unpredictable environment that is going to be challenging for your daughter no matter what interventions teachers put in place is the unreasonable approach teachers and other posters on this thread are trying to explain to you, and you just don't seem to see it.