According to the mtaphysics of this story, reality is multiple time-lines largely formed by divergences (splitting of time-lines), and these two characters are together in every time-line. Moreover, on some level, minds may become aware of alternate time-lines and even travel across time-lines, sometimes with a time-skip in one direction or the other, but something acts to preserve or restore the appearance within each time-line that it is the one reality. One device or mechanism involves people thinking that events which imply a multiverse are dreamt, rather than experienced.
It may be that the audience is intended to infer a merging of time-lines, but the more simple explanation is that the story ended with events in two previously unshown time-lines each of which had been affected by two other time-lines in which most of the story had taken place. The reason that this explanation is more simple is because a multiverse is already implied; a multiverse with simpler time-lines is simpler than a multiverse in which time-lines are themselves revised.
ah so she was in a parallel world with quite a bit of shit going on, but if the little one can go back to her time she can probably prevent everything for real