Ru had never smoked so much before but since she came to China, she had the urge to always hold a cigarette in her mouth. And that's what she did after leaving Lilith to decide her fate. She didn't smoke for cravings but rather she did it to distract her mind.
After smoking for a while, Ru went back to the courtyard and noticed the conflicted look in Lilith's eyes. Her eyes were stuck on the dagger and Ru was familiar with that look.
The reason she chose not to kill Lilith was simple; she didn't want an innocent person to die. And yes! For Ru, Lilith was innocent since whatever she did in life was done under the influence of drugs that had been induced in her body from a young age.
