It looks nice, so I'm surprised it doesn't have more comments here.
I like the clean surface and colors, even if these colors aren't much in the "melancholy way"
But the girl definitely is and her expression is so sad. Good work with the stuff flying out from her diary.
The only thing I would suggest to change is the grass or the sky. Because the sky isn't one of those realistic ones, but the grass seems to be quite in a natural way. You could try to compose the wall a bit better.

Anyway, this wall is good and beautiful.

Good work.