1) Was any part of Isa's room visible from outside the window at any part of the day? I'd say yes, considering the fact that the window is on the ground floor. In which case, easy enough for someone to make a note of which room in the house is probably that of the only little girl living in the house.
2) Why didn't Isa make a fuss? I don't know. Why didn't Danielle Van Dam? Why didn't Riley Fox? Why didn't a whole bunch of other abducted children make a fuss? Because some of them froze up with fear, some of them were being menaced with a weapon and some of them may not have awakened when they were being carried out. Some kids sleep very deeply and if they are used to being carried when asleep, it doesn't wake them up when someone picks them up.
I don't think the abductor left through the window. He may not have come in through the window, either; I think he popped the screen off the window and opened it just in case he needed to make a hasty retreat from the house. Like, say, if Isa had made a fuss...
3) I've owned 5 GSD in my life. They were all wonderful dogs but not one single one of them would have defended my property from an intruder. My person, yes; my property, nope.
Someone did try to attack me with a club and my first GSD pulled the leash out of my hand, took him down and stood on his chest daring him to move while I called the police. A medical examination of the perp showed absolutely no signs of any dog bites; apparently she did it all with the strategic application of her weight and her considerable roar.
There is a reason why PDs and sport dog people breed tons of litters and it's not because puppies are so irresistible. It's because it is a rare dog (1 in 10 or less) that will reliably attack a human being after extensive training.
That's one reason why more and more LE agencies are dividing up tasks between different dogs. It used to be an agency would have one dog that did drug detection, tracking and holding of suspects. It was so difficult to find dogs that could do it all that the prices were just beyond what most LE departments could afford. So they started dividing up tasks, buying dogs that were trained just to do drug detection, just to do tracking or just to apprehend and hold suspects.
Your dog may be exceptional and may defend your property in your absence.
I'd be willing to give her a go with my pocketful of garlic chicken. There's dogs out there that I can't handle but that is many fewer dogs than there are owners who swore to me I couldn't possibly handle their dog.
Unless specially trained (and most dogs aren't), the vast majority of dogs are opportunists. They love a "sucker" like me who gives away free cookies just for the sake of General Cuteness. The General must have incredible influence because I have yet to meet a dog I didn't think was generally cute.