Hot Car ...Free Flyer, MYDogIsCool.com I put one through the window to land on the driver's seat even in the winter. Even if I am watching the dog. Education could save a dog from suffering or dying. If I see a dog in a car during warm weather, I watch the dog for signs of stress until the owner gets back. If they don't come back quickly, I will call the police (but I haven't yet).It might be less confrontational to say something like "Thank goodness you are back! I was really worried about your dog in this heat because he looked distressed to me. You hear so much about pets and children dying in hot cars these days." And see where it goes from there.
Another way would be to hand her the phone and let her talk to the police, since they were already on the line in this situation.
I leave ice water and my car door unlocked when my dog is in it, in case somebody sees my dog in stress. I purposely save some of my trips until after dark so she can go. Also, I use my car that is parked in the garage because it is much cooler than the one that has been sitting in the sun all day.
They suggest that if a dog is overcome by heat to wet the dogs feet and coat with water and seek veterinary care immediately.
Your idea is very good too. But, I am not good at confrontation. Maybe, I need to get over myself and do it.