It’s a pretty classic Hero’s Journey:
Separation: Louise receives Call To Adventure taking her to the site of the alien ship, pulling her away from her Ordinary World and into the Extraordinary World.
Initiation: Her immersion in the language and by extension culture of the aliens pulls her not only into their experience, but into her OWN experience — glimpses of her future. Increasingly she has to rely on her own instincts, both intellectual and emotional, until she is the only person who ‘gets’ what the aliens are about, immersed in their mindset so she understands their experience of time is different than our experience. It’s her initiation into that mindset which allows her not only to unlock the key of what the aliens’ intention is, but also what the meaning of her ‘memories’ are.
Return: In literally coming back home, she now has a vision of what her future can be, and despite the pain it promises — losing Hannah, losing her husband — she says “yes”. This vision of home is the one she chooses to embrace.
As the Hero’s Journey, broadly speaking, has a tripartite movement, we can call it Three Act Structure because, well, it is. There are sequences and plotline points, but the contours of the narrative give us a clear grasp of the contours of Louise’s transformation.