What shadow does the death of Josie's sister Sal cast on the family and over the novel as a whole?

Sal, Josie's late sister, is said to have died from a disease when the girls were younger. What shadow does that loss cast on the family and over the novel as a whole?

It was a nebolous shadow in that it was never said exactly what she died from (unless I missed it!).it was like the elephant in the living room, but no one is talking about it.

I would have liked to know more about Sal. It seemed a bit mysterious. I could be wrong but was something mentioned that an AF was turned into an avatar of Sal and something went horribly wrong?

From what I understand is that the mother chose to have Sal genetically "lifted" but it back-fired and she ultimately died. They made an AF of her, but it was an early model which didn't compare to the newer editions...this is what Helen sees when she looks out her window.
I can't understand why the mother would choose to have Josie lifted in this way, knowing what happened to Sal. My guess is that Josie would have died as well, had Klara not gotten her the "solar therapy".

Sal was genetically lifted and died from the process. This is why I could not understand why the mother chose to have Josie genetically lifted. It seems to me that the mother’s concern with the family’s status in this society was more important than her daughter.

I have some questions about Sal that make conclusions difficult. How old was Josie when Sal died? This alters my answer - if Josie was lifted before Sal became ill, then the mother was in a sense trying to 'save' the only daughter she had left. However, if she knew what killed Sal and lifted Josie anyway, that seems very selfish to me - why lift when the potential of recurrence leading to a loss of the only child you have left - is it for status???? If so, I find that so terribly terribly sad.

Sal’s death was a dilemma set up to expose cultural norms of the day. Those with resources could afford to have a child “lifted”. I don’t think that meant Sal became an AI rather that she was genetically enhanced. Later, when Josie was old enough, perhaps the process had been improved but clearly it was an expected process to “get ahead” in the job market which would also reflect in status. Maybe in that world genes could be manufactured to make more intelligent people? Or more effective thinkers or idea processors? Or maybe it was misinformation and people were simply more willingly indoctrinated.

The family was still very much grieving Sal’s death. I don’t think the Mother thought she would be able to survive the death of her only other child. Sal’s non-presence was strongly felt by her family and her death had a big influence on their decisions. I don’t think it said whether the divorce was before or after Sal’s death but I’d be willing to bet it was after with the marriage not being able to survive the tragedy.

Having experienced growing up in a family in which a sibling had died, I can understand The Mother's concerns over losing another daughter to some mysterious illness. I did not actually connect the illness to the factor of being "lifted" as the concept of "lifted" was somewhat vague to me. But, the shadow of Sal's death truly dictated The Mother's actions and lent desperation to her attempts not to lose Josie entirely. That is why she was willing to risk Capaldi's experiment. I suspect that Sal's death was responsible for the estrangement or divorce from The Father as I have witnessed families in which this has happened.