The main feature that is included in girl beds is the availability of storage space. The bed that lasts through the teen age years can be filled with accessory spaces like for studying and for storing her cloths, make up items etc.
Of course, another aspect to a bed is its very size. Double beds (even childrens single beds) are large items. They dominate a small or even medium-sized room. It is imperative too that your bed is stylish and attractive, as well as comfortable. Nobody wants an eyesore in their bedroom, which is a highly private and personal space.