I think you can still get her by resolving Kagah's quest then ignoring the conflict. You still miss out on Halsin, but you haven't committed genocide either
Aaaaand the tieflings die because of your inaction. And you miss on the story. And XP. And loot.
There's so much more XP available in this game than what you need for level 12, it's not even funny. Please tell me you didn't actually pretend that XP is a even close to a factor in going for a fast evil playthrough.
