Den building in the woods,anything involving getting wet , or muddy, for a girl maybe making some simple clothes, or anything requiring glitter and glue. Check out the works for cheap crafting ideas, painting pebbles (acrylic paint is best). A picnic buffet them to help preparing the food first, baking cakes ( from a mix is easiest but get lots of extra decorations)
Contact an association for dwarfism in your area. They should be able to help you. Swimming lessons would be practical, a local park with inclusive equipment, maybe roller skating.