SPOLERS AHEAD

The girl tries to keep herself updated via a diary for years, but eventually the information about this life she lived but can't remember becomes overwhelming (requiring hours to digest and come to terms with, repeated every day) and too disconnected from what she does remember. She asks her parents to simply lie to her and act as if nothing had happened and it really were the day after the one she last remembers (i.e. one day earlier for every day that passes) and there's just some unexpected problem that prevents her from going to school, meeting her friends, have a birthday party, etc. (since it's SF, it's possible for the parents not to age).

The parents agree, since watching their daughter struggle with that mind-boggling revelation every day anew had been painful, but the resulting charade is in some ways worse, especially after the mother dies in an accident.