I think you’re supposed to take the fact that she can "see" ("experience" or however you want to put it) her future at face value. Chiang has been pretty forthcoming about that point in Arrival interviews, and I think it’s meant to be a sci-fi trope (Star Trek, Vonnegut) reformatted as a literary tool, a kind of reflection on life. It’s a hard line to walk, for sure, and I think you’re right that film hits it a bit too hard to make the point whereas a book can be much more subtle, but Arrival does a great job I think in illustrating what it would look/feel like to view time that way.