I love time travel movies but it's so inconsistent in this movie. Changing the past changes the future, but only when it serves the plot. The main character would never live in the house where her father got killed so she'd have never made contact with crazy girl, this is just one example but there's so many paradoxes in this film
shareThere are many. But after she returns to the house once her father is killed (disappears from the car) you can clearly see that she is not living in the house anymore and it's deserted. When she left with her father to drive, it was in a different state altogether.
shareIn the new reality, her father is killed in the house in front of her eyes. So why would she grow up and return 20 years later and talk to the crazy girl who murdered her father? It's the Grandfather Paradox, and I'm willing to overlook it for this discussion.
But the OP is right, the rules of time travel are very inconsistent in this movie.
For example, in 1999, the crazy girl murders her mom instead of vice-versa. This changes the future. In the altered 2019, the main girl reads about the crazy girl's arrest even though it is yet to happen in 1999. So the rules of time travel as per this major plot point are that though certain new events are yet to take place in the new 1999, its consequences will already have happened in the new 2019.
OTOH, certain other plot points imply that there is a real-time connection between 1999 and 2019. That changes in 1999 will directly mirror consequences in 2019. For example, the strawberry farmer and the dad don't disappear from 2019 until the very moment the crazy girl kills them in 1999. In the final act, everything the crazy girl does in 1999 leads to spontaneous changes for the main girl in 2019. Which is different from the newspaper headlines scenario, which implies that all actions in a new reality are pre-ordained.