Huang Rong did threaten her to stay away from Guo Jing with a knife. If Nianci fell for Guo Jing and refused though, what do you think Huang Rong would do? Would she carry through with that? Which raises another question. Given her selfish and sometimes cruel behavior (I recall her once brutalizing a fat peasant who did nothing to her) do you think she would have been able to win Guo King’s heart without her incredible beauty? It was she, after all, who started hitting on him, am I right?