I believe that Mom was so focused on SS not being home when she said she would, Mom needed her vehicle that very next morning and she probably knew at that point that it wasn't coming home and had no clue where it was, SS was intoxicated, and Mom was likely a big ole mix of worried, sleepy, frustrated, had to get the other child up for school in a few hours, and she just didn't think to zone in on those around SS in the vehicle. I'd guess, that SS's mother, didn't think that was the last time she may talk/see her, so she wasn't scanning for clues about the vehicle, or the other riders, jmo. She may have asked, Where on earth are you going at 3:00 a.m.?! and gotten an answer, It's all good! Don't worry! (or something similar). Edit; I think I jumped off the wrong post, but ya'll get the picture.