From the floor plan link, it looks almost like she's had to have let him in the door. If you go to the Redfin links, the way it looks, her bedroom was either downstairs on the lowest level (one article talked about blood spatters in an office, iirc), with the office, and there's a door there, or, it's on the upper floor, and I think the windows would be too high. The deck seems accessible to the Master Bedroom but not so much, to the other bedrooms. Some of the plans are flipped so you have to visualize them upside down. I downloaded some of them to flip them on my laptop.
ETA: There are five bedrooms. Four all together on one floor and one on the lowest floor, with the office/den space that walks out onto the patio, from what I can tell.
Those are pretty nice windows and doors too. Sliding doors are quiet as well.
Oh, and me too, rowdy kid, but I'd never dreamed of sneaking a boy in my room! I'd much rather got caught sneaking out or in. To get caught bringing a boy in, would have been unforgivable. I doubt I ever could have looked them in the eyes. I never even partied there if they left me alone. But I was so willful, that I had to break free. I just couldn't help it. I respected my parents enough that I didn't want them to know what I was doing but I just had to do it.