What is ironic about the dog's response to the woman in "Ah, Are You Digging on My Grave?" by Thomas Hardy?

I think the irony of it is that the mistress thought that her dog loved her more than anyone else. Based on the poem, everyone in her life had moved on and had lived their lives as if she has not died. She thought that at least someone had remembered her and tried to pull her out from her grave, but to her dismay, her dog only dug her grave to bury his bone.