I'm a bit confused as to what's going on here...
Her rabbit died while she was on vacation. She wakes up hungover, says she has to hurry to catch her flight, but should have time to clean the rabbit's food and water dispensers and cage. But in the bottom panel of the first page you can see the water dispenser and the food bowl sitting empty on top of the refrigerator, with her forgetting to fill them and put them back in the cage with the rabbit. The ending has her returning to her apartment after apparently cutting her vacation short to go check on her bunny, who is almost certainly dead of dehydration.
Everything between that is kinda muddled, but I think the black rabbit they have to swerve to avoid is actually the ghost of Rope, who at this point is dead and is probably a vengeful spirit but an angry bunny ghost is pretty limited in what it can to do to get revenge, so has to settle for trying and failing to get them to drive off a dangerous mountain road.
And then there's the revelation that her mother asking about the bunny is what makes her realize that she forgot to leave it food and water, but if her mother realized she had forgotten to drop her pet rabbit off before she went on vacation shouldn't she have said something sooner? Like, say, in less time than it would take for an unattended rabbit to die?
So the gist of it is that a moment of negligence resulted in the death of her pet rabbit, and that's the scary part. How it gets from that premise to the reveal is... questionable.