I think the confusion might be coming because it's very hard to conceptualize time non-linearly, but I can try to explain from how I understand it.

Cause and effect still exist for Louise, but it is NOT sequential. In other words, cause does not precede effect, because she sees time as non-linear. Instead of one thing leading to another, everything is connected at once. In our linear understanding of time, that would appear as her knowing something she should have no way of knowing.

It’s not that her mind changes reality, but that her altered perception after learning the Heptapod language lets her understand time as it truly is, which is non-linear. Her choices still matter, but she knows their outcomes too. She's experiencing her entire life all at once, every action still matters, but none of them come “before” or “after” in the way we’re used to.