I thought in the movie it was cast as her choosing to accept it and cherishing the time they'd have left together? Maybe I missed the predestination theme (or maybe it was just implied... although you could say it's implied for any story involving travel or communication between different times.)

We’ll I certainly walked away with an understanding that it was all predestined, which annoyed me to no end because it felt like a ridiculous and meaningless cop out. But maybe I misread something that was actually more ambiguous?