If we consider the possibility that Serenity's motivation for running was an attempt to go home – and I don't get any sense that her flight was that organized; I think she was running 'away' because of some emotional overload, not 'toward' anything in particular – I doubt that at age 9, having lived in this facility for a relatively short time, she would have the faintest idea in which direction to travel, much less a specific route in mind.
IMOO children at that age have no real sense of mapping or direction beyond their immediate neighborhood, and don't think point-to-point so much as "Let's go to the (playground, ice cream shop, McDonalds)" – then let an adult figure out how to get there and follow the adult's lead, or amuse themselves with games, chatter, or music while the adult is driving. From what I've seen, they need repeat exposure to walking (or biking) routes before they feel confident using them on their own, and tend to fear themselves lost rather quickly if they find themselves in a little-known area without a trusted adult. Just my own experience with chaperoning elementary-school-age children, and as a former child myself.
JMO
edit: punctuation