Spoiler warning: Spoilers for the complete film.
Lou is Philip’s mother, making her Vee’s grandmother, and the ferry’s final watcher strongly indicates that she survived. Her role in the rescue is therefore personal long before Hannah understands the connection.
Why was Lou living beside Hannah?
She is a former CIA operative who rented her property to Hannah after Hannah fled Philip’s abuse. The supposedly isolated neighbor has placed herself near the family her own son threatens.
Her intervention is not simply an expert lending unusual skills to strangers. She has a responsibility within the history Hannah is trying to escape, even if she has not disclosed it.
The reveal also changes Lou’s emotional distance. Withholding information has allowed her to remain nearby without asking Hannah to accept her as family.
What happens in the confrontation with Philip?
With a CIA sniper overhead, Lou pulls Philip close. They are shot and fall into the water without surfacing in that scene.
Hannah subsequently finds that Lou has left her the property. She sells it and leaves with Vee and Jax, receiving a practical means to begin elsewhere rather than only the memory of a rescue.
The inheritance gives Hannah a choice Lou’s secrecy had previously kept out of reach: where to live once the threat is no longer deciding for her.
Is the woman on the ferry Lou?
Jax notices someone above, and the closing image reveals a woman observing Hannah and Vee through binoculars. The sequence is constructed as a survival reveal, although it does not explain every detail of how she escaped the water.
That missing mechanism should not become an invented account of a staged shooting or an unseen extraction. The ending supplies recognition, not the operation behind it.
Lou’s continued distance is also consequential. Surviving does not mean claiming the place of parent or grandparent in Hannah’s new life. She can watch the family leave while allowing the rescue and the property to give them independence from her as well as from Philip.
Sources: official ending breakdown.