The thing I love about D&D is that you can take anything from anywhere, and then just throw it out the window and start over.
Maybe in his world, Half vampires are a fairly common thing, so people WON'T run in terror from them. Don't force yourself into the preset mold, D&D is about playing an interactive story.
No, 1/2 Vamps are very, very rare. There are a fair number of people that have some vampire blood in them, and full vampires aren't totally unheard of (some are even 'good' guys, though since I don't use a fixed alignment system, good is relative). As far as the group knows, however, this player is the only 1/2 vamp in...well...ever. Of course, she's not the only 1/2 vampire, she just doesn't know that yet.
That's a grand idea. Reminds me of Shanarra kind of in the later supplements. I convinced my DM to introduce airships into his world and created a Eladrin SwordMage that was a hydrophobic airship pirate that has a teleporting addiction (4th Ed).
Heh. My policy for what players can, and cannot do, is that they can try anything. That doesn't mean it will work. Perfect example of this is when my 1/2 vamp (who has a high charisma, added to which is a limited bonus from being a vampire) and rogue needed to assassinate a base commander. Their were 2 guards outside, and 2 guards inside, plus the base commander. But they only knew about the 2 guards outside and the commander. However, they wanted to kill the commander in his sleep, so the rogue stealthed the 2 guards outside. When they opened the door, boom, there were 2 very surprised looking guards looking at them, hands on their weapons. Improvising, the 1/2 vamp pretended to be a hooker, and proceeded to seduce the guards. One of them apparently lost a little too much blood to his brain, and fainted. The other was so focused on the 1/2 vamp he didn't notice the dagger in his spine until it was too late. All without waking up the commader. That went down in the 'book of epic moments'. Took us 15 minutes to stop laughing long enough to finish the mission.