I agree, it is hard. I never let my DD do dangerous things alone. I even ended up driving her to and from school because I caught her taking rides with older friends a couple of times. The bus stop was t the bottom of the hill at an intersection where a lot of our friends lived. They would literally stop a few feet away from where she was standing for the bus, so of course they would offer her a ride. And I didn't like her riding with new drivers.
But I was mostly referring to the statement that they are not going to allow their 15 yr old to go anywhere on their own, for safety sake. I think kids need to be on their own in safe locations to learn how to make their own decisions.
I agree that she might have agreed to take a day trip with someone and they turned out to be evil. Or it could be a landscaper or local employeee or a neighbor even.