I've been lurking here for a bit, but decided to post some of my random thoughts.
Regarding the neighbor- I tend to believe she did hear what she says she heard. I'm just not positive that she heard Isabel being taken, if that makes sense? Our neighbor's house is very close to ours and there have been times when their outside activity has woken me up- talking, car doors slamming, etc. I have never once bothered to get up and look out my window, and I don't blame this neighbor for not doing so. And I totally understand what she's saying when she says it was daylight, so she didn't think to look. If I heard the same noises that I've heard in the morning, but at night time- you bet I'd be looking out the window. Somehow daylight makes them seem...not nefarious.
About the dogs at 6:30- I have 2 dogs. Often times when we let them out they RUN out in the yard and start barking up a storm at something we never noticed- a rabbit, a neighbor sitting on their deck, a kid walking to the bus stop. Given the time line, my theory is that the mom let the dogs out before work, and the dogs immediately knew something was up! They were barking up a storm (which maybe got the neighbor's dogs barking) because they knew something was wrong. If an intruder took Isabel, they could smell the intruder in the yard.
That said, I don't understand how dogs that are supposedly very vocal managed to...not make a sound while Isabel was being taken. Makes me suspicious, to be honest- I realize we don't know for a fact that they didn't make a noise. I guess they could have been shut in the boys' room, or with the parents, etc. Or maybe any barking they did do was ignored because they always bark.
I don't know. On one hand, I very much can see how the dogs barking at 6:30 was the dogs trying to alert the family that something was wrong- not saying they heard or saw anyone (though I think that's possible, still- perhaps the intruder took her to the red car?), but I can't necessarily make that work with an intruder managing to come in the house without alerting the dogs. Hmmm.