It's not that our Essence is "better" than a Laywoman's, but the fact that we have access to a nearly endless supply of it. Marius had screwed himself into the Mana-Curse equivalent of Stage IV cancer, and most traditional healers would have run out of juice before they could put a dent in it.
It could be that she's right and the only thing special about what she can do is the pure amount of essence that she can pour into things but she could be wrong as well and given that large amounts of essence could be covered by using more then one healer working together I was wondering if there was something else there. That something else could be that the sisters of virtue are Mana healers rather then essence healers because essence healers get tithed or it could be that her essence sight was a bigger factor in her healing than was shown. I only felt that there was something there that was more then more power.