I do agree with the previous comments.
But I was also thinking, so basically ara's supposed to die, the timeline isn't supposed to be changed and ara's never supposed to be alive at the current time, so she's gonna keep on running into situations where she's dying. But since big sis can see the future, she's gonna have to keep on saving ara at every hour until she reaches the current time because I think the timelines can possibly converge and ara would be alive.
because the phone is definitely messing with the timelines, if it can reach into another timeline it maybe can alter timelines too.
So basically she has to keep on changing the past until the past reaches the point where she receives the phone (which is like what, 3 years??)