My daughter's room is 2 shades of pink with white rectangles framing out the walls. I wanted to give her a princess room that wasn't specific to princesses so it could be whatever she wants and would grow with her a bit. I'll see if I can dig up pictures, maybe it will give you some ideas.
I did my daughters room in purple.. with green trim.. and accents. at her age.. I start with bedding.. look some up online.. a lot of times they have a bed in a bedroom that is themed around the bedding.. let her see what she likes and go from there.
she said girl colors LOL so I am thinking pink, purple etc