He is using different definitions of soul in that passage. So, I agree with Raisins.
There is a soul that is eternal I believe, which you never lose.
There is a soul that is about maintaining oneself, one's identity, one's conscience even while wearing a mantle.
There is a soul where doing bad acts causes you to lose it.
Mab ability to maintain her soul "depends on who [she] is going into it and what kind of will [she] has to maintain who [she] is", but her mantle has warped it to such a degree that Jim himself can't really tell if she has a "conscience" left which is I believe the test case if she has lost her soul, her identity separate from the mantle.