both my DD6's do the same. Their narrative is at the level of about a 200 word story but they rethink every sentence and reconstruct before writing into simple language to avoid errors. It took me a while to work out they were doing it. They also have a dictionary but they find the children's dictionaries never have their words in them and adult dictionaries too intimidating/difficult/time consuming. They do type but their typing speed is way below their writing speed but they do find the computer spelling options handy.
My only solution so far has been to pretend I can't understand a sentence that is missing complex descriptors. So for example if they write "the pink princess" I would say "oh what a nice character for a story an ugly princess with awful pink hair" they of course respond "no she is beautiful" and I let them know "no she is just pink that sounds awful maybe write beautiful or goregous instead". This seemed to get the message through to them that simple words, although enabling correct spelling, did not enable the reader to understand their story.
