My DS says the same thing. He loved preschool, so I am trying not to worry. Hopefully this is just an adjustment period. It does take some time to get a class up and running, especially kindergarten, in which there are probably a few kids who have never been to school before. There also are a lot more kids in his class (25 total) than there were in preschool, and I think he misses the chance to frequently interact with the teacher.
My DS is also pretty advanced as far as academics go, so if they are doing simple things like letter recognition, he would be bored stiff. I don't actually know much about what he does in class, because when I ask, all he claims he can remember is what they had for snack! I am trying to relax about it until Curriculum Night in late September. If they are working well below his ability, and not adapting some material for him, then I will push it.
Hopefully your daughter will settle in and feel good about it in a few days. I think it's probably too early for any of us, kids or parents, to judge at this point.