What she gained by "going back in time" is being able to stalk/love him again until she had to kill him to possibly repeat the process. The entire manga has strongly pointed to her being completely insane obsessed with him. If the plot twist which was heavily hinted at by information the main character uncovered (and this is different than predictable by the way), you guys should have been able to guess yuno's motives as well since they were there in every damn chapter.
