We ended up spending most of the visit drawing together, and by the end of it, I'd drawn a pumpkin, a basic pine tree, and the picture below upon their request, as well as two new symmetrical patterns.
Grandma also drew a couple patterns. I don't have permission to share them on the internet as a whole, so for now they're only available to my inner circle on Patreon. But here are the pictures I can share:
The photo didn't have the lightning or snowfall; those were added afterward upon my grandparents' request.
This picture was drawn freehand with a mouse, and I didn't really touch it up afterward, so there are a couple messy patches, but I like the way it turned out overall.
If you want to learn how to draw symmetrical patterns like this, I've got a handy tutorial for you here.