I guess the writers wanted to keep us in suspense about the outcome of Burke's peremptory orders to Vicki. But it would have been fun to see Vicki give him an argument for a change.
Maybe Sarah simply doesn't associate the tombs with her parents, or at least not directly. She's looking for her friends (and relatives), but she probably assumes they're somewhere on the same plane of existence as she is, and all she has to do is find them. Still, it is a bit strange that she has David stand on her mother's tomb. She probably doesn't even realize that she's dead, much less a ghost.
And I don't think Sarah has any idea that she might be putting David in any danger--she's just achingly lonely. Her main motive for bringing him to the cemetery is to keep him with her a little while longer, and the best way to do that is to get him curious--after all, who can resist a secret? And David thought the first one she told him--that Maggie Evans was alive--was a real humdinger.
Our first sight of Sarah is in connection with Maggie, but I suspect she was watching Barnabas for a while before that. His behavior must be utterly incomprehensible to her.
My notes indicate that when Julia arrives at the Old House, Barnabas remains seated as he says with great formality, "I apologize for not rising to greet you, but I’m not feeling well." Even though he threatens to kill her in every other sentence, he has already started treating her less like a servant. You can take the vampire out of the eighteenth century, but you can't take the eighteenth century out of the vampire! Even so, he still finds her self-assurance extremely annoying. But even that annoyance is a very human response.
Great ending as David finally helps Sarah raise the coffin lid and they stare down into the coffin….
