Because that's the one sword that was given to her by her father, as simple as that.
Show me the Enma gimmick in action in either of the two scarring scenes please, both Oden's Paradise Totsuka and Zoro's Dead Man's Game.
The attack scarred Kaidou because it was laced with CoC as Kaidou literally talked about, that's all it is. The rest all of your arguments are just smoke and mirrors.