So if that day she wants to work geometry, language, projects... she writes everything down. Then I take a look and see if we cover all subjects, if not, I suggest. If she doesn't want to work on what is missing, then we write it down on the next page for the next day, because the subject has to be covered. It's a way of doing things.
Another way, more spontaneous, is that every time the child does something, he writes it down in his agenda, and at the end of the day, we can go through it to see what has been covered throughout the day.
One way or the other is good, it all depends with what method the child is comfortable with.