>>114921041presumably human, because it requires being dead to become a zombie instead of merely being healed. Thus the risk is too high, after all they have no proof that they could recreate the effect on the spot. The only it way it could ever happen, is if she happen to die early in her life by an accident or some villain/monster, but never by choice.
BUT since they will be fusing a lot and make out and fuck all the time, it''s fair to assume that her body will be constantly regenerated from his body fluids, meaning she will always stay young anyway, as long as Steven is around.