Girlfriend has shouted at me in public for the first time

Hi,

I've (30m) been with my girlfriend (26F) for four years. We've just spent a really nice day together. At the end of the day she wanted me to take some photos of her. She wasnt happy with how she looked in the photos that I was taking so she made a few suggestions which I followed but they still weren't good enough. She was getting more and more annoyed with each photo so I told her that she was getting a little bratty in hopes she would just leave it and we could go home. This only caused her to be more confrontational as she began telling me how terrible I was at taking photos.

I eventually had enough I said that she was acting childish which was beginning to ruin a perfect day (I already know that it was wrong for me to say that). She didn't respond well to this and began shouting and swearing at me in public. I tried calming her down by explaining why I lashed out but she just kept telling me to shut up and that she'd had enough. In the end I just stayed silent, she drove me back to the car and we have both gone back to our own houses.

TL;DR! - I would say this is unacceptable behaviour but I wanted to know if what I said warranted this sort of response? I'm terrible when it comes to arguments because I always doubt myself.