Hi SH,
The first few weeks at school are for assessments and getting through some of the required basic teaching concepts. In our local schools (in Valencia), once the teachers have determined what levels the children are at, they break them into groups based on their academic needs and give them work that will challenge them at their levels. So don't worry about how easy it is, it will get more challenging and she will begin to learn new concepts.
As far as lacking music and other creative stimulation, grade schools often do not offer much of this in their standardized curriculum. Also, grade school teachers are required to take completely different courses than preschool teachers when going to college, so they are not exposed to a lot of Child Development concepts, which preschool teachers use to make learning fun. Since she can no longer expect much fun in her school environment, your daughter might benefit from taking outside enrichment classes offered in your community, or you could make up a music program to do with her at home.
As far as cheering your daughter up, I would reassure her that she will soon start to learn new things as school gets going, and that now is her chance to get to know her teacher and the other students in her class. When she comes home after school, ask her to tell you about her day and the interactions she had with the other children. Also, share with her what you remember of your experiences in school. Let her know that she will be in school for many many years to come, and she will learn that she likes some parts of school better than others, but that it is important for her to work hard and stay focused in order to be successful.