And such assurances Carissa can provide, carefully, at length, because 'what actually happens to people when they go to Hell' has been something of an urgent priority for her, and by this time they've made secret information-purchases on many, many related questions. She did not deceive Abrogail, as to what would have happened; only as to whether it did.
She does not know, not for sure, not without seeing it unfold before her, whether she's made someone trustworthy, out of Abrogail; someone who would betray Asmodeus for a goddess who, technically, hasn't ascended yet. Abrogail will have to think about it herself, with the clarity that almost no one in the world could bring to bear on the question, if she wants to ever leave this room.