User blog comment:Xilinoc/Ch. 591 - Marching Out the ZOMBIES 2/@comment-24113610-20140730121824/@comment-1338810-20140730123115

"-I think Giselle has to have them ingest her blood before she kills them to make them actual Zombies."

She doesn't. She stated outright two chapters ago that all she has to do is splash some of her blood on a Shinigami in order to zombify them. After all, Shinigami are souls and therefore are already technically "dead". Meanwhile, all Quincy start out as living humans, so it makes sense that they actually have to die before zombification occurs.

Now if Giselle killed Hitsugaya before zombifying him just because she could? That I would believe.