Lol you guys.... 

When i first built this character, she was actually a phsycic vampire permanently stuck in mist form (classic vampire power) that was until she honed her phsycic ability to "posess" others minds and regain her body back momentarily... That was the ORIGINAL character for a Vampire bloodlines game waaaay back in 94' :)

Taking note of your wishes what if we meet somewhere in the middle of the road? Lets say she is a Vampire but an old one with extraordinarily power phsycic abilities that got captured and experimented on until she could no longer sustain a physical body due to lack of blood sustinence during capture. That in turn almost killed her without help from experiments done to her via the human side.

About the killing to survive part... I dont believe i stated she needed to kill to survive, matter of fact her hosting with Roman keeps her well and dandy, its the natural instinct and euphoric feeling of her sucking the life essence from another that she craves. She doesnt NEED to do it but she really WANTS to. (Exe you dont need to have that piece of chocolate cake but you really want too lol) The host only dies because she kills them out of pity, she shares her mind with them and naturally they cannot handle the pressure making them go insane. (Hence her immense phsycic power) 

In short... What if i just say shes just a Phsycic vampire without a physical body stuck in a mist-like form? Also, although she remembers many things from her life as well as her fallen prey, she has major problems deciphering what she used to be thanks to the jumblefluck of memories in her mind with no "physical" mind to process them... Except for Romans of course :)