12. So she does some time lord god magic and merges all timelines into their origin point at the baptism, and drowns Booker, preventing him from ever becoming Comstock and eliminating all relevant realities
Ahh! This has been confusing me since I finished the game earlier today. I was wondering how drowning Booker would affect all the other timelines, but now realizing she has the ability to merge possible worlds makes it all make sense now.