Hmm, the sub reveals a whole lot of plotpoints, here are my speculations on the whole thing.
Seems like both Sheryl and Ranka were artificial constructs or atleast bred/born in tube to specifications (think Qwisatz Haderach from Dune), with Sheryl likely being an improved model but didn't have time to "mature/evolve" as the previous Ranka model. Furthermore the speculation about it being an AI uprising a la butlerian jihad or maybe even forced Cyborg evolution might be true.
Depending on if their comment that Macross Frontier is targeted as it is one of the rare fleets that have outlawed cyborgs means that they attack it because of them outlawing cyborgs or because they are at a serious disadvantage because of them outlawing cyborgs and therefore an easier target to hack into unnoticed.
Sheryl might also have the illness because she has a built-in limited life expectancy. Sort of like the replicants in Blade Runner. Perhaps the Witchcraft pills were used to accelerate the process. Don't know how the earrings fit into that, but them belonging to her "mother" sort of makes sense now
Yeah, the loss of ambient pressure would mean that the water would quickly start to boil and freeze only a short time later. Loss of artificial gravity would also likely have caused the water to disperse depending on inertia of the out of control habitat.