As a matter of timing, Lee Mok Sau's murder of the Luk Family in Gong Nam couldn't have been worse. She chose to commit the murders the night before Gwok Jing and Wong Yung arrived in town. Moreover, West Poison Au Yeung Fung (from whom she stole the 5 Poisons Manual several years earlier) was in the neighborhood as well. Indeed, Lee Mok Sau nearly didn't escape from a through-passing East Heretic Wong Yerk See in the end (she was damn lucky that Wong Yerk See got distracted by Ching Ying's injury). Of course, Lee Mok Sau had no idea that all these Greats were in the area, but if she did, would she have thought twice about attacking that night?
What if you were Lee Mok Sau and you knew that the Gwok couple, West Poison, and East Heretic were all in the vicinity of Luk Family Manor? Would you go ahead and slaughter the Luks anyway, or would you wait for the Greats to leave town?