Ending question, the physiatrist talks about how she wants to get to the lighthouse because "she" wants to get there and not whatever "she" would become. Then Kane says he THINKS he used to be a man named Kane, but he's no longer sure and his mind has been splintered. This is telling us that while the Lena that got out is the same as the one that got in, she was changed and mutated so much that she's no longer the Lena but just a splintered and mutated version of what she once was, right? Obviously it's not 1 to 1 but it's kinda like a Ship of Theseus type of deal, yeah? Or did the ending go completely over my head, that's also likely.
I wonder if Lena at the end was really the clone (who lied and killed the real Lena and set the lighthouse on fire). Or perhaps Lena's DNA had changed in the shimmer so much, she's no longer simply Lena anymore (hence the eyes at the end). Shame she was never once called Ghost Bird.
I'm of the belief that Kane on the outside is the clone, due to the video and his body failing (the shimmer hasnt perfected cloning human dna 100%), but that the Lena we see is the same we see throughout only mutated by the shimmer due to her time there. She doesn't have the light in her like the novel, the physciatrist seems to have that covered, but she has been changed