How does she get home at 5pm? Does the school offer a bus service at that hour?
And as bizarre as this might sound, outside of New York City, unaccompanied children on public transportation is basically not a thing in America. We assume the children are lost / abandoned and the parents are delinquent / trying to get the kid kidnapped by a pedo.
There was a decently widespread news story a few years ago about someone calling the police on a mother because she let her kids go to the park by themselves.