She was killed by being pushed into the fireplace by her right-handed, not-extremely-strong sociopathic psychopath spouse who was having an affair? And here I was suspecting the clerk, but it all makes sense now.
I think that if they did live in a post-apocalyptic world, Red, her mother, and grandmother, and possibly cyberjack, would live together, not separate. Safety in numbers.
The murderer was a schizophrenic stranger who was Mr. Peach's business partner? What kind of business was the victim involved in where he didn't know his partner?