Mag Chalkboard Paint: Paint a wall, have some craft activities to have her make castle/house/outdoors/etc pieces (modular ideas so she can build the castle in many different configurations). Also could use chalk to outline and draw.
If you haven’t seen the viral pictures of English artist Julian Beever’s work, then you aren’t on the web enough. Mr. Beever started as a street artist who figured out how to make his pastel chalk drawings on hard sidewalks turn into three-dimensional scenes that amazed and delighted passersby. Beever started out with traditional paintings but soon figured out how to give his work a three-dimensional twist and those pieces became a web sensation.