In Act 2, Saheila is being held by the lonewolves in a logging camp to the north of the elf camp. She is in the second floor of the east building. You have two options to getting to her;
1: go through the front gate and talk your way through the lonewolves, thus gaining access to her without a fight.
2: Sneak pass everyone to get to her. (This can be easily done if you go through the back east gate. Sneaking out is easier if you open this gate prior).
Though the achievement tells you not to kill anyone; you can kill the men guarding her. Once she joins your party, take her down stairs and select her. *You dont have to escape with her for the achievement*. Once your sneaking take a few minutes to study the movement patterns of the lone wolves before advancing forward. Take your time and quick save whe n your at a safe spot; incase of errors. *if you sneak out the back dont kill her with the traps*. Once shes out just run away until she leaves your party and this achievement is yours.