If Lina left by foot...
Last summer I remember driving on Gardendale as a shortcut on my lunchbreak and there was a group of kids scurrying across the street eastbound to the apartment complex on the other side of Gardendale. About 8 of them, no adults, ranging from about 5-10 years old. I've seen this else where in the medical center, and the kids are usually carrying a soccer ball, sticks, or really small siblings. I can easily see how an unattended child could get led away unintentionally by a group of children, through several apartment complexes and across a street.
If she left by foot, Fred Rd to the West is too busy to cross, with exception of the drainage easement that runs under Fred @ Hamilton Wolfe and that would have put her in the WellMed parking lot at a busy time. USAA fencing on the North is restrictive, and Wurzbach borders to the South. Someone on the roads would have reported a lone child, especially at 5PM in the MedCtr. There are just too many good, smart people driving by that would have called it in or at least remembered her. But a specific child amongst a group traversing eastwards in between buildings could go unnoticed and quickly reach the greenbelt and woods behind Limestone Oaks. Along the way the way there are no intersections with cameras, just older buildings, parking lots, cars, and dumpsters. I've read SAR stories on how far a lost child can travel across rough ground through the woods. She could have covered a quarter mile east in ten minutes, if running with other kids.
Your thoughts sleuthers?