You can pick one color off the wallpaper and paint the other walls that color. Paint the doorframe and the windowframe another color off the wallpaper (ex: pink for the wall, blue for the frames). If you have shelving in the room, paint that yellow.
Or ask your daughter which colors in the wallpaper she likes best and figure out the wall/frame/shelving color combo from there.
You can also make a project out of it and do one wall one color, one wall another, and one wall yet another, all with colors off the wallpaper (one pink wall, one blue wall, one yellow wall). If you plan on doing the painting yourself, make sure your daughter can feel like she is helping out in the project- have her paint a center portion of the wall which she can easily reach (but you take care of the walls down by the floor!)