My best guess for the part where she is floating in the swimming pool is that she has been brought back into desperation over her husband and children's deaths. It represents her hopelessness and pure emptiness at that point, like she wants to give up or is paralyzed (like she says later). Also,the snow I think is just a representative for the movement of time and change as the end of the movie approaches. I think it is meant to be a symbol of a new outlook. change in all of their lives.
That is my best guess anyway. But also, if anyone can please explain the whole 21 grams thing at the end to me that would be great. you could email me. I just don't get it. I thought I knew what it meant until I actually saw the movie. How he says it confused me. Please help.
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