end of spoilers
Not saying I'm sure it's Lash, but there was still a connection between Harry's Soul-Spirit self and his physical form during Ghost Story. He was able to taste Mab and smell pine while he was in the graveyard talking to The Famous Ghost of Graceland. So she could have still been powered by his soul, I guess. It could be that the Lash shadow kept his heart beating(If he had a heart after being shot through the chest.) Butter's body did require CPR until his soul was returned. Why Mab and Lash would both be required for the CPR ministrations doesn't make great sense though.
Unrelated: In Dead Beat, Mort had shaved his head bald and moved out of his California-style Stucco house. In Ghost Story, he's living in the California-style and this is the first time Dresden sees him sporting the full-on Charles Xavier. Just a goof?