Once you have found Sasha in the Ebon Hawk, tell her to go away. Keep saying go away. Once she starts to run away, catch her before she can leave and repeat this process. If she gets too close to the door, say ''A little girl? How did you get in here?''
Then say ''Don't worry, I won't hurt you.''
Then, ''Err....okay, whatever you say.''
Repeat this whole process until you have the level you want. I did this and it took about 5-10 minutes to turn completely dark from about 3/4 down. You can only do this when you talk to her the first time, before you get off the ship on the next planet.