The in thing right now for girls rooms is wallpaper stencils which are also removable. You can get them anywhere from Loew's to wal-Mart. They stuck right to the wall but are separate pictures. Follow her favorite theme and change it later.
A simple way to get creative and not go overboard is to pick two colors, one slightly lighter than the other. Do the walls in sections, the lower section with the dark and upper light. Do the trim opposite of the wall color. Where they meet, try a delicate border.
It depends on your daughters age as to what designs are appropriate. But the "tattoo" look in designs seems to be very popular with most ages, featuring a solid color with a swirly, somewhat floral look as a one-color silhouette on top of the solid color.
It's been my experience that girls love the lastest trends in color and fashion. My ideas for girls rooms have come from the lastest issues of teen magazines. If she is interested in fashion, I would stencil some clothing designs on walls. Younger girls prefer butterflies,horses etc.
I would recommend something she can grow with, so paint the walls a bright solid color (bright green, purple, etc. ) and then add accessories according to her interests now. Stripes and dots are something that she can definitely grow with, and not outgrow quikcly like princesses or barbies or something like that.