A view from the top, as best I could-
If you were standing over the top of her gravemarker, that little hole almost appears to be a keyhole.
How fascinating it would be to be able to have that key.
Not that it opens anything, there is no mechanism for the key to turn.
I think it was made just for a keepsake for the family.
As I have said before , if I were not so opposed to being buried, this is the gravemarker I would want for myself.