According to state law it was illegal only because she was under 18. If you think about it the cage part was safer than if she was sitting lose and might fly/fall out of the bed.
"Twenty states have no laws prohibiting riders in the back of pickup trucks. Not surprisingly, most of these states contain substantial rural areas where pickup trucks are needed for work uses."
"The following states allow back riders older than age 18; Florida, Georgia, Maine (older than age 19), Michigan, Missouri, Nebraska, Nevada, New Mexico, Oregon, Pennsylvania"
http://www.attorneys.com/traffic-tic...k-of-a-pickup/
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