Howdy today sir free-reign! Yes, I wonder what the circumstance was that made her break out in such a smile. I've read a couple of articles about why no one smiled in the photos from the 1800's. They were instructed by the photographers to be as regal and serious looking as they could because they wanted to preserve that image for future generations.. that was one major factor.
The other factor was that without modern dentistry most people had bad teeth!