Your friend has been very good at training her dog but to get a dog to this there has to be lot of solid obedience work as well as a high level of respect. It is of course the ideal that every owner can down their dog from a distance, whatever the distraction. This is not something that can be taught to a dog overnight (or to an owner!). It is also assuming that the owner is with the dog every time a truck is around. Tying a dog with such an ingrained habit of chasing could cause the dog quite serious injury as the chase instinct will almost certainly over-ride the knowledge of the tether. An enclosure, or keeping the dog in the house is really the safest way of dealing with Daisy, at least until you are confident that her remote down is trustworthy in the face of such a distraction.