I am responsible for my wife's mother's death? My wife thinks so!!!!!!!!?

Nothing has really been the same since my wife's mother died in a car accident. I was her driving her home one night but I was extremely hungry so I stop by a Burger joint to get a hamburger. I was short on time so when I left I did not tie my wife's mother with a seat belt. I started to eat while i was driving because I was hungry but I unexpectedly drop my hamburger. I reached down to retrieve it but when I look up I notice I was about to run into a truck. Just then I swerved to avoid a collision but I ran off the road causing the car to tip over. I came out fine but my wife's mother died. I wife is really mad at me and says she wants me to rot in jail. Her mother was old anyways. So how can I make her see it is not my fault!!!