During Lee Mok Sau's decade-plus rampage across wulin, she had only limited contact with the Greats, and she was fortunate that they were either uninterested in killing her or fate intervened on her behalf. West Poison Au Yeung Fung would have killed Lee Mok Sau had her teacher (the unnamed second generation Ancient Tomb Sect Leader) not rescued her, and Lee was lucky *twice* against East Heretic Wong Yerk See, with circumstances saving her life from the Lord of Peach Blossom Island.
Lee Mok Sau never encountered South Emperor 1 Deng (except very briefly just before her death), and the benign monk would not have broken the non-killing commandment on her account. North Beggar Hung 7 Gung, however, was known to kill individuals he deemed evil. Before the Second Mt. Hua Sword Tournament, Hung 7 Gung famously told Kau Cheen Yan that he'd killed over 200 evil men during his career as a wulin hero, and that he would not hesitate to make Kau the next one to die. Clearly, Hung 7 Gung did not believe in being merciful towards evildoers.
Lee Mok Sau never met Hung 7 Gung, but had she encountered the old beggar, do you think Hung 7 Gung (unlike the other Greats she encountered) would have just killed her for her evil deeds?