Juliet's sister never had cancer in the ALT by JohnConstant69

This rests and builds on my other theory (815ers are original island gods) saying that the ALT isn't really an ALT at all, but a new birth-cycle, or new incarnation. The forgotten island gods, the core 815ers, most of the Oceanic 6, go through time-loops, or reincarnations, over and over, until they can change, as the numbers, and save the world.

When Desmond says to Jack "see you in another life brotha", its a literal prophetic fulfillment which we saw on the plane.
Jack REALLY sees him in another life, another carnation, another cycle. As the MIB said "it happens over and over", and as Jacob said "but it only ends once".

Basically the island is a nexus between all realities or incarnations, and its possible to bump into another incarnation of yourself. All worlds, realities, and incarnations connect to the island. This may explain the whispers, some peculiar behavior from the Others (who I think may be able to crossover the realities), etc.

So when Ben had Mikhal "Patchy" show Juliet the footage of the "cured" sister off-island, it wasn't really Juliet's sister, in the main sense, but the ALT sister, in the other sideways-flash or cycle (yeah, the terminology gets difficult).

That sister never had cancer in that other reality, so, no, Jacob nor the island ever did anything for her. Juliet was duped. Ben had Mikhal cut off the "live feed" real fast so Juliet could not see any more context to the footage.

I'm not being dogmatic about this, but it occured to me this could be yet another interesting little tidbit that the ALT can resolve. Of course this all just a theory.