I randomly remembered a book I read probably a few years ago now. I only remember a few oddly specific things.
For starters, this main girl had a brother and she would bring food out to their yard to him and that is just always where they met up. By a tree, I think. Then later we find out that the brother is actually dead and she has been imagining this all. And the food she was giving him in like these sandwich bags is her food and she wasn’t eating. So she sort of accidentally starved herself. And I think at a point near the end, the parents see all of the sandwich bags full of food out by the tree and sort of realize what has been going on.
That is all I can remember, I hope you can help!!