Was the nanny evil?
I don't get it.
Did the nanny kill her own child ("I got my soul back")?
Was she cursing Laura with the charms under the crib?
Laura had post-partum depression everything she saw in the world was skewed making it seem darker than it was.
More realistically the nanny used some old fashioned charm that helped her feel better and was a good woman.
Laura was simply sick and as a result thought everythig was evil. At one point she even felt that about her husband.