Was I wrong?

I live in a state where the weather is brutal in the summer. Very very hot. I know better than to leave my child in the car in the summer time, even for a minute. It was 95 out today. I drove to the gas station with my daughter who was promptly throwing a temper tantrum because I said no candy. I opened her door and she screamed at me that she wasn't going in with me. I told her fine, you can sit on the sidewalk your not staying in the car. She sat there under the shade by the door on the sidewalk pouting while I grabbed a drink. She's 6 years old. I could see her and still hear her crying inside. This lady stops in front of her outside, says something along the lines of who are you with? Then bursts through the door demanding who's child is outside. I claimed my child and she goes off on me in the store saying how dare I leave her out there unattended and I was a terrible mother and that she was going to call the cops. She never did, I told her to mind her own business and drove off. I don't feel I did anything wrong. Opinions?