I think they were visiting the vampires grave. Otherwise I think she'd have visited more than one. I want to think her cousin and the girl are just old and still living. Which is why they came back to visit.
I think that long-lived vampire was dead because it was mentioned that vampire will live only for a thousand years. When that vampire appear in this story, he was already live for more than 800 years, if I'm not wrong.. I think many years has gone since that girl became vampire's partner (I forgot their names), so maybe all human that they know already dead and only those three that was left behind. Sorry for my broken english
Ending is so confusinggggg. Did that long-lived vampire actually die? I'm assuming the high school girl with dark short hair pass away due to old age? What about the doctor-to-be cousin? Ugh. Too many holes.