I think I read that Celina's family has a dog or dogs. Hard to imagine in a house with several residents, no one would wake up at the sound of the dog barking (that sound is much more likely to wake most people than other kinds of noise), which I think would have happened if someone was hurting Celina in the home. For that reason, I think she was taken away from the house in a vehicle, and that's where she was either killed or brought somewhere remote to be killed.
I'm no expert, but if in fact she was wrapped up and then put in the water, it goes to depersonalization of her and that IMO would be a result of rage, not horseplay gone awry.
BTW, does anyone know which of the house's occupants goes to work other than LN?