I spend a little time with Mercy and legend tripping behaviour in What Happens Next? Contemporary Legends and Popular Culture (page 48). Two of Kiernan's earlier works are annotated: the novel The Red Tree (2009) and the short story "As Red as Red" published in Haunted Legends (2010).
Kiernan, writing as Tierney, has her narrator Quinn say this about the gravesite:
The tombstone's nothing fancy, a slab of marble with dates of birth and death, just the usual. Visitors had left a random assortment of tokens lined up along the top of the storn: pennies, small stones, a pewter pin from the Newport Folk Festival. In front of the stone there was no grass at all, just a dirt patch worn smooth by long years of the feet of those who came to see. The letters engraved in the marble had become ever more indistinct as a hundred and sixteen years of rain had eaten at the stone. Another hundred, it'll likely only be an anonymous slab. But maybe I'll still be around, and I'll remember.
The stone was securely bolted down with iron bands and concrete to ensure some damned frat boy, goth kid, or eBay huckster wouldn't try to make off with it (241).