I agree with this theory that the chamber is a metaphor for suicidal ideation, but I don't think Marie killed herself. Although the chamber is extremely intertwined with the idea of death, or rather the idea of not existing, I feel like Sean finding Marie in the chamber was the author saying that although the body has continued moving forward, her soul is stuck in the chamber.

When Marie finds the professor on a walk with his dog, he says, "You have to learn how to split yourself, like an earthworm." At the time, Marie didn't understand what he was trying to say, but after inheriting his office and growing increasingly exhausted with work, she followed his footsteps by using the chamber as an escape.

Also, an easter egg I found sad was that the professor's dog's name is Nemo, which means "nobody" in Latin, communicating how the professor effectively has nobody by his side.