D.H.
If she likes princess's and fairy's go with a theme of that sort, there are all kinds out and you can find paper, and decorations just about everywhere..........and they like those even at 7 or 8......
If you want something more grown up than that, you could go with musical notes, or if she likes sports, some sports stuff........
Go to a paint store or a hardware store and see what they have.......sky's the limit...........if you can draw, put drawings on the wall and paint them, if not, there are people you can pay to that..........
good luck and have a great day.