I just saw [b]Swimming Pool[/b] and I'm confused . . .

Like the title says, I saw Swimming Pool today and I’m confused by the ending of the movie. Can anyone who’s seen it explain it to me? I’ll probably add spoilers later on. Thanks.

Only an opinion, but:

Nothing that happens in the movie is real after she goes to France. It all exists in her head, for the book she is seen writing. When we see the real publisher’s daughter morph into the fake sexy daughter at the end, that’s the tipoff.