You see, Miriam sees how you're going to die. Throughout the book she sees countless future deaths, always insisting they can't be changed because of one incident where she took the active approach (instead of just telling people that they're going to die which, let's be honest, who's going to believe the crazy chick telling them that in seven years and three days they're going to be run over by a car?) and failed spectacularly.
Since that moment, she firmly believes that death can't be stopped, and she's just a spectator of it. She stops trying, and even starts to profit off the deaths she sees.
But at the end of the novel, she discovers that to stop death SPOILERS!
