What the Screenwriter\Director said.
The interesting interview can be found here:
http://www.francois-ozon.com/en/interviews-swimming-pool
He may not necessarily clear things up for all, though he does give credence to much of the "it's Sarah's imagination" theory, but from what he says, it also could be construed that the Julie character is not entirely of Sarah's imagination, from his following remark:
"Sarah Morton needs solitude for her work, she needs to lock herself up in a comfortable house, go on a diet, live by certain rules. Then all at once, reality bursts in on her. Her first reaction, needless to say, is rejection. She turns in on herself. Then she decides to incorporate this new reality into the work she is engaged in"
To me, this seems to suggest that perhaps the Julie character arriving at the house and the initial interactions between her and Sarah may have been in Sarah's "reality" realm of the movie, and that which follows (after she creates the "Julie" folder on her computer) is of her "imaginary" realm. share