From everything I've seen (the video walk through of the house), the door could have been opened up a small amount, enough to see out of the bedroom and look towards the living room or towards the stairs that lead to the third floor.
I think it's entirely possible that he didn't see her. It was 4 AM or so in the morning, assuming that it was fairly dark inside the house. Also, the affidavit doesn't say that DM saw him walk out the sliding door - it states that "The male walked past D.M. as she stood in a "frozen shock phase." The male walked towards the back sliding glass door."
I don't see why it's not reasonable that she peaked out her door, saw him walking towards her as he was coming from the direction of the living room and walked by her in the direction of the kitchen. MOO is that she peaked out that door and saw something she did not recognize or expect to see, stood frozen trying not to draw any attention or make any noise, and after he passed by her she then closed the door and locked herself inside.