When I was a couple years younger than Abby, myself and several other kids had quite a long walk home through our neighborhood from the point where the school bus dropped us off.
I was acquainted with these kids through school, but I wouldn't have called any of them close friends. One of the boys had noticed that a large home across the street (on a wooded, dead-end street) from his home was empty. It was a nice middle-class neighborhood so it wasn't an 'abandoned' home, just empty for the time being (no furniture, or residents. Possibly being prepared for sale or being remodeled?). For some reason it was always left unlocked. Anyhow, the boys in our little "group" somehow enticed us into sneaking into the home with them on several occasions after school when we were walking home. Everyone's parents worked, so nobody knew we didn't walk straight home. Nothing sinister happened, as we were quite young and it was both scary and thrilling to even have stepped foot into the home for five minutes.
Looking back, it was stupid and I would never do something like that now (It was years and years ago, I was about 12). But I guess my point is, none of us would ever have dared tell our parents or other friends that we had been sneaking into that home.
I am not suggesting that Abigail did anything similar. I just think there is a lot of wiggle room for what kids may do, or what situations they may end up in on a long walk home. There still could be a lot LE doesn't know.
That being said, I tend to believe Abby was picked up in a vehicle by an adult.
JMO