It was a bit hard to determine who's talking, and I guess reader had to follow the story in DiPP. If someone can understand the story please let us know.
Not sure at all, but I'm guessing it's a fourth wall thing. I think Flan sees the painting and it's the expression she's making in the last page, causing her to actually make that expression. I think she's realizing that she fell into Jacket Girl's trap and that Flan did help create something: the story of the doujin.