Focus on a white floral area rug for a young girls bedroom

13 year old's bedroom?

If you plan on a dark color, you have to lighten up in other ways. Are the book shelves built ins? If so, you need to work with the shelves and the dark floor. A good theme to work with if you like white, purple, and flowers would be to focus on lilacs.  

Lighten up your floor with a white area rug. This Modern Ivory Area Rug has flowers, and would look great against that dark floor

I always recommend a collection of stuff on one big wall that helps you organize your room. A large bulletin board, a grouping of picture frames, a place to put your souvenirs, etc. When you create a central area in your room for everything, you will always feel organized.

It looks like a fairly big room, so be sure to give yourself a little corner for reading. You might want to add a pretty white and purple bean bag chair.