Organize all those baby stuffs and toys that were stored in the room in a cabinet and decorate her room with some big girl’s stuffs: you may use fashion items like, hats, bags, shoes, watches, and other grown up stuffs. In choosing fabrics for the room, you may linen, denim, silks, and with designs like, stripes, checks, hounds tooth and toile.
You may place furniture in her room like; dressers, tables, chairs that are strong and durable. Get her a toddler bed or a full sized bed. If she cannot reach the bed because of its height then you may provide her a step stool. It would be better if the designs selected would be classic, this will help her more feel that she is indeed a grown up girl. You can add a cabinet with good books to read, there are books that can purchased that will give them tips too to act a grown up girl or you can place the books that she also likes.
Train her using women accessories, like earrings, bracelets, watches and buy her clothes that will suit her best. Train her to beautify herself with a good dress up and pair them with good accessories. Give her comfortable pillows and blankets too. You may want her to have an adult comforter in her bed as well. Moreover, those are the tips your little girl in a grown up room.