So your hypothetical is that someone reads the headline "elderly woman kills family of four with car due to incapacity, receives no jail time" and goes "oh, no jail? No biggie" but if they read a headline "... and receives life in prison" they're going to rush out and take away grandma's keys because now they care?
Really?
The message that incapacity, even to the point of killing four people, will be excused is quite clear.
The deterrence argument is used to throw the book at people committing minor crimes like shoplifting. Let's apply it to quadruple homicide, eh?
Mary Long Fau should have died in prison.