rickman, sorry to hear this, it must be worrying for you...just wanted to add that my ds has started reception 3 weeks ago, and he has certainly been grumpier, more prone to tantrums etc; when we go to the park after I pick him up, he is so different to his normal self, he is usually very imaginative and chatty and talks nicely to anyone, but after school he is 'roaring' in people's faces, telling them to get out of his way, poking them etc!!!!
I do think school is a huge adjustment for them, and very tiring, specially for your dd who is already full time - my ds only goes for 2 hours a day!
I definitely think you should just run all that you have said here, past the head; no head will mind you checking these things out in view of how unhappy she seems. Also, someone on another thread said that they treated reception as almost another pre-school, in that when their child seemed very tired, they just kept them home for a 'duvet day'! I would keep her home on occasion when you feel she is exhausted, though obviously not so much that it affects her ability to settle. But I certainly mean to keep ds at home if I feel he needs a rest.
Also agree being a parent helper for a little while will give you an insight into how things are done at the school!