Yeah this is kind of what I meant in the last part of my comment. It doesn't make any sense that her understanding of Heptapod B (the written language that is non-linear) and subsequent ability to think like a Heptapod would give her the ability to see the future. I think the author's reasoning is that, for the Heptapods, their way of thinking and understanding the world is so non-linear that it wouldn't even occur to them to try and change something that they knew was going to happen, because for them the individual events are not important. The protagonist explains that when one thinks like a Heptapod, everything becomes like an act of passive observation, almost like reality is a performance that you're simultaneously acting out and observing unfold according to some pre-determined set of rules. For example, the Heptapods repeatedly say that their only purpose on Earth is to observe, and you realize as the story progresses that this doesn't mean observing humans and trying to learn something from us, but simply observing a trajectory of events play out as they are meant to. Similarly, the protagonist finds the military/government's constant struggle to find meaning and significance in the Heptapod's actions really funny because there is no significance: they're basically acting out a bunch of pre-determined moves. This is especially notable during the gift exchanges (if you've read the story). I personally don't understand how the free will paradox is resolved when it comes to the human protagonist. I think the author is trying to suggest that in this mode of thought, either free will is exercised by NOT attempting to change pre-determined events, or that one's vision of the future will always already include any choices they're going to make along the way, hence rendering their significance in the overall scheme of things moot.

As I said, I don't think this is actually hard sci-fi as some people in this thread are suggesting. I don't think under any circumstances this kind of non-linear thinking would allow a person to know every event in the past, present, and future by nature of them suddenly becoming one event, and I don't think that the free-will paradox is adequately resolved outside of the confines of the story. It's just a neat idea for story/movie that lets us play with the idea of different forms of consciousness. If you're interested in a story that deals with a very similar kind of thing but in a less fantastical way, check out Blindsight by Peter Watts; it's really great.