O Captain, My Captain

When Tom Weylin dies in Dana's care, it's a very important turning point both for Rufus and for Dana.  All the times that Dana had come back to antebellum Maryland, she was always able to cure what was ailing Rufus or anyone else.  All of a sudden, she didn't cure someone, and it wasn't just anyone, it was Tom Weylin whom she'd had run-ins with before.  Now realistically there wasn't anything Dana could have done to save him, he had a heart attack, which even with modern medicine is often fatal.  Dana knows this, and deep down Rufus knows it too, but the mirage that she is this guardian angel figure is gone.

Rufus now is forced to see that Dana may not always be there to protect him and the plantation.  Even worse, she can now be seen as a threat.  If she didn't save Tom, why would she save Rufus?  Rufus doesn't know that she's a descendant of his, so seemingly the only thing making sure she saves him is that his father would have tortured and killed her if she hadn't--a thing Tom reminds Dana on multiple occasions.  He knows that when he's in danger of being killed she comes against her will, but once she's there there isn't anything stopping her from walking away from him now.  Rufus has to give in to Dana a little more, because unlike before, she now holds a lot of the cards.  While he's alive and lucid she is still his slave, but clearly he never knows when he'll be near death so he can't take the chance.

For Dana, she's now had someone die on her watch.  As traumatic as it must be, it's liberating too (irony fully intended).  Tom's death gives her the leverage to inspire fear in Rufus of what she's capable of.  It also proves to herself that she can survive in that time with someone's death.  Her parents died when she was young, so she knows what that loss is like, how debilitating it can be.  I think she was living still in a little bit of a fantasy world that nothing was ever going to change around the Weylin plantation and she would always just be getting Rufus out of jams and playing him against his father.  Now that fantasy is over and she's now gained an even stronger position in that time.  Going forward, things will be different, and the unspoken understanding between Rufus and Dana is going to be even more sensitive.