One has two possible solutions to solving the Doreen quest: convincing her to leave peacefully, or killing her. The first solution yields double the loyalty bonus in Drassen.
Sirtech's intention was that if you kill her after already having solved the quest, you lose the loyalty gain you got for the peaceful solution. But due to not taking into account twon sentiment properly, the bonus was never fully removed. As a solution the optimal approach was to first convince her of the error of her ways, and then to kill her. Which, frankly, shouldn't be a thing. The population shouldn't cheer you most when you convince someone to do something for you and then immediately stab you in the back.

Fixed in r8835.