Reveal My Destiny
The quest will start right after Jaethal arrives at the throne room to give you bad news. You’ll have to meet with the elves in their camp. Bring her into the squad and head for the camp. You’ll find it on the left part of the region, next to the river which flows between you and Pitax. Go there, talk with Jaethal’s daughter and decide their fate. Jaethal may even disappear from the squad.
This will happen only if you convince her that she’s become a monster. That way you’ll meet Jaethal in Nyrissa’s house in the seventh chapter, and Jaethal won’t kill Tristian. More importantly, she’ll return to your squad.