I'm just going to be frank, because from what I can tell, your a family who will understand what it is I do.
I'm the medical examiner, who is also a Zombie. When there is a case that needs solving with no clues, I eat the brain of the dead to figure out what happened to solve the case, to give them peace.
No one was sure how the fire started, I know the answer.
The AI she was working with, Callister seemed to have short-circuit, which caused the fire. It happen fast, too quickly, and that's what happened.
I'm truly sorry for your loss and I'm sorry for being so blunt, I just wanted you to have closure.