What makes it really funny is that the dhampir in question is a bit of a MAD SCIENTIST. So she doesn't really care for the supernatural (I mean, look what it did to her) and she's very much a creature of the Enlightenment. Unfortunately, she lives in the World of Darkness... Also, vampires can be a symbol of more things than just sex and plague. I've seen a universe where they could arguably be symbols of, say, mental illness. I happen to rather like vampires-as-tragic-heroes, just sayin'.
That does sound really interesting. I'm not sure how the supernatural and the scientific fit together in the World of Darkness, but I think it would make a very interesting read.
You're right. They are symbolic of multiple things, yes.
I hope you all realize that I'm going to be rather noncommittal about the vampire symbolism though. I think there are a lot of reasons people choose to write about certain things, and I choose not to place more importance on one over another.
For instance, young girls are also in a very vulnerable place, and they could write about vampires as a bit of a power fantasy (a powerful creature deferring to a young girl out of love, giving her the power, or even the girl herself being the vampire [and lots of other variations]) like people have pointed out about why some young girls write super powerful Sues.
A lot of reasons for a lot of things. Vaguity vague vague. But true.