He is actually XXY intersex, or at least it's implied, but he's also half-vampire on his mother's side. The entire point of this exercise is that he has a vampire instincts but a human body, and that will drive him insane eventually. So his parents took the AI/Game they were already working on and added a feature to allow him to subconsciously choose which path to take, either a male human or a female vampire (since the vampire trait is in the XX bits). Whichever one he chose, the 'Cradle' he is in will reformat his body to match. Since she chose female vampire, that's what's she's going to be when she gets out.
