Some Dark Brotherhood and general game spoilers.

So in the dark brotherhood, muiri asks you to kill her ex bf and a member of family she used to be friends with, but after an incident, the mother, (tova) shuts her off. So Muiri asks me if maybe I could also stop by and kill Nilsine, Tova's daughter, to show Tova how much Muiri means to her. So I'm like, okay, I'll kill Nilsine. This is very early on in the game. Much later, having gathered my riches, I want to by hjerim, my favorite house, and settle down. Only problem is, Tova, whose daughter I murdered, seems to be the only character in the entire game that is saddened when a family member dies, and kills herself. But she's essential to Nother quest, blood on the ice, required to by hjerim. A terrible coincidence. Has anyone found a way to start blood on the ice without her, or console commands?

You should start the quest by walking to the crime scene and activating the scripted event, however there might be the possibility that you walked near the crime scene and triggering the event without you knowing. If you start the quest this way talk to the guard and follow the quest line