When decorating a girl's bedroom, you need to consider not only the age of the child, but the rapidity with which she will grow into new, more mature tastes. Therefore, it is necessary to make permanent things in her room (floor, walls, bed, furniture), easily changed or adaptable, and leave the "theme" to items such as appliques, throw rugs, pictures, curtains, bed linens, etc. Her tastes are going to change. Plan your decorating with that in mind at all times.
Your little girl wants to be a princess. So buy some of those wonderful, peelable appliques and apply them to her headboard, the cornice above her window, and the toy box in her play corner. Posters can adorn her walls to carry out the theme. A small coronet attached to the ceiling at the head of her bed with some pale tulle draped to her headboard, a matching dust ruffle, a princess doll laying on her bedspread, and your daughter will believe her room is her kingdom!
Bookshelf Toy Storage
As your precious adolescent reaches her teens, there is a change in attitude. She now thinks she IS a princess, and wants that reflected in her room. And this can be easily done, since you were so farsighted in your decorating.
Remove those appliques, take down those childish posters, and remove the play table in the toy corner. Replace the fairy princess fabrics from her canopy and dust ruffle. Replace them with lace, or whatever style she is now into. She might like plain mosquito netting for her canopy, and a fluffy quilt on her bed.
That toy box can be painted and used for storage at the foot of her bed. Go to a flea market and pick up a little table, chair and a framed mirror. Spray paint the table and frame whatever color she loves at the moment. A nice cushion on the chair and your princess now has a dressing table.