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The 3 Elizabeth versions :
1) The first version is the regular one (scenes 1 to 19, Elizabeth in her blue outfit)

2) The second version can be seen after waiting for a while at the end of scene 19 until the rift opens (as described before, unlock scene 20, Elizabeth from the Burial at Sea DLC)

3) The third version is shown in a short scene that will play when your "salts bar" is empty at scene 19 and that you try to restart to scene 1.
Elizabeth will tell you that "you're low on salts" and she will help you to replenish your bar (unlock scene 0, Elizabeth when you first met her in the game).
Only scene 19 will reduce the salts bar (after the cum scene), so you can just restart until your bar run out, or you can hit "v" on your keyboard to reduce your bar manually.