You seem to understand most of it. That's what happened.
The most likely explanation for Elizabeth having powers to fukk with reality is because she was the only person to exist in 2 realities. Not different versions of her, the same her. Remember part of her finger got cut off and stayed in Booker's reality, the rest of her went to Comstock's reality.
Also there isn't just 2 versions of Booker. If you play the DLC "Burial At Sea" it takes place after the game, and there's another version of Booker.
Fred.
Elizabeth was not the only one to exist in multiple universes.
the founding fathers existed in multiple universes, so did Booker/Comstock.
for whatever reason, Elizabeth has the ability to break tear into other universes...nobody really knows why or how but they are ready to take advantage of it.
the founding fathers existed in multiple universes, so did Booker/Comstock.
for whatever reason, Elizabeth has the ability to break tear into other universes...nobody really knows why or how but they are ready to take advantage of it.

as the final cutscene played out. I argued with my friends about the ending of this game for 2 weeks when it first dropped.
And is it me, or are the Burial at Sea episodes a lot harder than the actual game? You barely get any ammo. Well it's not really that hard, just the difficulty spiked up and made things frustrating. It's becoming more apparent playing through the second ep just now. Scarce ammo and guns, and it feels like it's becoming more of a stealth game now more than just a first person shooter.
Keep creeping up behind them being a headbusta!
It's been so long since I went through the actual game so I can't remember how they compare tho. 



at all the tie-ins/callbacks i missed