I would suggest to add a function so you can add a personal note to each day, and sell it as a mood tracker / diary. First, it would be useful to keep track of why you were feeling bad or good on a given day by maybe a making a small not on what happen. Plus, then apple would not be able to reject it, as it would be a diary app with a graph. There are a ton of diary apps on iOS, and this one would even have a graph. Let them argue that's not novel and feature reach :)