In act 1 I pretended I would open the grove's gate and then betrayed Minthara. In the battle that followed I knocked her out and killed all the other assailants. (Robbed her weapons and armor)
In Act 2, I let Ketheric send her to prison. When I found her in prison afterrwards, convinced the interrogators to let me handle it and then linked with Minthara to push the absolute's mind-torture out.
The inquisitors were surprised and then I opted to attack them together with Minthara.
After they were dead, Minthara became "plant-like". No conversation possible, no movement from her side.
So meanwhile all absolutists in the prison and on the docks are dead. The thieflings and gnomes are saved and in moonlight inn. I took a long rest, returned to the prison and Minthara remains in the same unresponsive state. The marker for the quest "decide on Minthara's fate" is still there on the minimap.
