After drowning Booker to destroy the cycle that creates Father Zachary Comstock, Elizabeth found herself wandering about different dimensions and realities, watching and observing what is and was, a collection of memories from the other hers that ceased to exist with the drowning of Booker becoming hers until she couldn't quite remember what it was she wanted all those years stuck in that tower, imprisoned by the man that was both her father and not.
Was it Paris she wanted to see? Did she want to be free? When she opened tears to see through into other realities, to travel into them, what did she seek? With Columbia ceasing to exist in any reality, with Zachary Comstock being only Booker Dewitt in every universe—
What is she to do? What is her purpose now? What is she to do now that she's drowned her father, Booker Dewitt? Her father, that sold her when she was an infant yet fought to get her back before his mind was hazed with half-memories and lies, scrambled in the haste of being thrown into another universe for a second chance to save his daughter? He is dead yet alive and she's seen it, peaking into the new universes created by his martyr and drowning. Made a martyr twice, now in these new realities he is happy, with his dear daughter Anna safe.
Elizabeth wishes she could live that life with Booker, that they could have had that chance— she thinks to the ups and downs they had when he came to save her, unaware himself at what really he was doing or what he was there, in Columbia, to do, memory a haze from interdimensional travel. But she can't have it.
She wants to live, not read, not look, not observe— none of that, just being, is all she wants now. But she's never just lived, has she? So how does she?
She finds herself looking through the vast expanse of all the universes heart ticking with uncertainty and under-stimulation. She closes her eyes, takes a breath, and lets herself fall into the grasp of a universe she's never touched or looked at as another Elizabeth, or as herself.