The Grim version was published in 1812, but it's based on older stories. Here's one published in 1782 that also features a mirror:
https://en.wikipedia.org/wiki/Richilde_(fairy_tale)
However these are both just published versions of oral folktales. The basic outline of the story might go back hundreds of years earlier, and nobody will ever be able to say when the mirror first showed up.
To the extent that I'm trying to make a point, I think this supports it!
> By the time Richilde is fifteen, she is an orphan and the new Countess. Her dying mother warned her to be virtuous and never use the mirror for frivolity
This is something that would be a lot harder to synthesize in a world where mirrors are abundant, and the link between self-reflection and vanity is strong here.