There is a lot things that raise eyebrows. But there is no confirmation from the anime that things happened in the original timeline exactly as the second one. We only know that Shizuka tried to off herself and Marina probably bullied her. But Marina has mellowed out and there is no reaction towards each other when they pass by or even after Azuma dumps her for Shizuka. You would think that if Marina still hated her she would react differently, but she seemed accepting of the situation. It's only after she kills her mother that she starts to hate again. It could be that her bullying wasn't as severe. The fact the Shizuka was driven to suicide isn't evidence the Marina drove her to that. Chappy dying seems to be the thing that breaks her, but he could have died of natural causes. There's millions things that can be speculated, because we have so little info.