I haven't played the 'evil' route in a while and only once at that, but I remember failing that persuasion roll, did they change that in one of the patches? I like to think I treated her well too, though I was roleplaying a lolthsworn.
Or just become a companion; there is already a plenty of reasoning for this to happen. Even for non-evil playthrough.
I'm not sure how non-evil runs don't end up with her and the rest of the goblin leaders being dead? And If you bypass the whole conflict you won't have spoken to her in the first place.