Well, Mami's wish didn't change; she was still the survivor of a car accident that would have killed her. And I still feel that she has some of the lowest possibility of becoming a witch, what sort of despair would overwhelm the wish "I want to live" other than the sort of suicidal despair that can overtake anyone?
dctreborn: Madoka's wish wasn't to not become a witch, she had left the opening for her to become a witch, recall that there was a moment where the bright shining comet of her Soul Gem was enveloped in the darkness, until she revealed why her hope would win.
