Let them study, explore and codify their findings. Charlotte Mason fans all know about nature journals. Girls especially, enjoy writing about their observations of birds, weather changes, seasons and other critter visitors. Help them include accurate labels. Encourage descriptive detail.
Girls seem to like relationships and friends are the best source.
They also like to describe people and scenes related to people. Sometimes this topic is a total dud. But when there has been a unique experience associated with a holiday, the child can at least hook into something specific and write about it. Star Wars, Star Trek, Narnia Chronicles, Redwall these are inspiring kids to make up their own worlds. When they are given freedom, they will often attempt to duplicate what they read.