Interesting note about her as well. My fort is in a very homogenous world and everyone has silver eyes and mahogany hair ... but the vampire has WHITE hair and none of the wrinkles that come with age. You can use this to help identify vamps.
Mine has gray hairs with sepia. However, since vampires tend to knock about the world their appearance can be different from the rest of your dwarves. This won't help finding patriotic vampires.
Now about the suspect ... it's just an oddity. It is a dwarven child who is 14 years old. He SHOULD have grown up by now ...
I have one 13 years-old. Right now, when I've looked into his description alcohol withdrawal syndrome scared the shit out of me, but then I realized that ALL my dwarves experience it so not 100%
it's a bug, they're clear
Vampires seem to be distant in relations with others. Since I've renamed his profession via therapist to draft him and didn't notice that one recruit is missing he's been chilling in the meeting are for a long time and still has only passing acquaintances.
Also, someone has already mentioned that undead and vamps ignore each other, thus, first (maybe only) dwarves that get to the entrance in evil biomes are risk-group. On the side note they make good woodcutters.