The opening being at an angle would be difficult to exit. In your precious post side view, it looks like a drop down to ground, on a steep incline. JMO, it would be hard to straddle the window and drop, in just underwear, without her getting scraped up.
I think the bedroom doors were closed to the parents room to keep out the critters. Nora came down to the bathroom and encountered someone who took her. That person may have caught her coming out of bathroom, covered her mouth and walked her out the front door. I don't see an easy exit thru the window, even if she did walk off, why go thru the window when she could open the door. The doors have no locks per the website. Everyone was exhausted and just didn't hear anything. JMO