The problem I think is that most work at school is rather easy and she is not challenged enough. When I try to get her to do anything which requires effort and thought on her part she doesn't want to know. I'm now of the opinion that children are not being taught to think and really consider options, so much so that if the answer doesn't immediately come to mind they can't be bothered to think it through.
I had the same thoughts when my son was at primary school. He is good at maths, but at first we had deadlocks and tears with the 11+ when he was not finding something easy.
I got round the problem by breaking down the difficulty, making up easier problems and building up slowly towards more difficult ones. It worked fairly well as long as I was being very careful to avoid a crisis of confidence.
Now that he is at grammar school, he is absolutely fine.