We do not know how Corey is able to alter what she did on July 1st, but we already know from the first film that someone within sight of the future end of the vortex can send a message to his earlier self, and regretting the death of her friend Sam, Corey does this. It does not create a different anomaly, because both the message and the car depart from the future and arrive in the past together. However, it creates two other problems.
The big problem is that Corey has killed herself. That is a problem because once she does this, she cannot do it–a grandfather paradox without the generational complications. In this history, Samantha is not killed by the car, but Corey is. Samantha mourns the death of her friend, but has no clear way to leave town immediately and no clear destination. Billy’s ghost does not appear to anyone other than Corey, and with her dead he cannot lead her to the future to send the message to herself. Thus she never sends the message, and if she never sends it, she never receives it, and we have an infinity loop. If she lives, she sends the message that causes her death, and if she dies she never sends the message and thus lives. Our story ends here.
Some will attempt to resolve this with some version of an understanding of Niven’s Law, that once a time traveler changes the past the past remains changed even if the time traveler never makes the trip to change it. Apart from the logical problems here, the film later relies on the notion that if you eliminate a temporal departure you eliminate the arrival–that is, in the final history of the world Corey will not receive the telepathic message regarding talking to Samantha because the past has changed, but that must mean that it did not arrive because it was never sent, and therefore a message never sent will never arrive, exactly the situation we have here.
The smaller problem is somewhat awkward, something of a butterfly effect problem, which we will address next time.