You know it's hard to convince a young person to wear a helmet. Not because they are stupid, but because they don't believe that anything bad will happen to them and they think they are invincible. I remember being that age and younger and never thought about something bad happening while riding my bike. I didn't wear a helmet as a kid, and my parents didn't even think about getting me one. Of course I grew up in a different time but although the times are different kids are pretty much the same as we were when we were growing up. They have more toys, electronics and just more stuff in general, but they really are, all in all the same. They think their parents don't know anything, they think they are invincible, they think they have all the time in the world, they think if they mess up it won't be a big deal and they have plenty of time to fix things.
I'm sorry, I don't think she is stupid, she is just ill informed, or hasn't been taught any better. Having a policeman for a husband I know too that parents rather than take responsiblity for their children and teach them from the beginning to wear a helmet will do just what these parents have done and use scare tatics making the police the bad guys rather than tell their child she will wear a helmet or won't ride the bike. This girl was just smart enough to call and ask rather than believe whatever her parents tell her.