Actually, I doubt Sheryl's a cyborg at all. I think the alterations made to her were genetic. Remember the dialogue in the recap episode about her being Fair # whatever it was, in the abscence of having Ranka around, they fiddled with Sheryl's body/DNA to give her the same properties of Ranka (likely the Nome Shamen gene).
Something tells me this is all going to tie in with the flying rocks that you all hated from Zero. But it's obviosuly a process which isn't difficult for Grace to perform, since she wasn't too concerned with loosing either Sheryl or Ranka on Galia 4.
Right now it's looking to me like there will turn out to be some kind of Protoculture Midiclorians, either the virus/crystals in Ranka's belly is the component passed down in the Nome family that lets them control/use PC technology, or something along those lines. Jumping back into pure speculation, the whole deal with the V-Virus may be that Mao's DNA wound up slipping into the populace during the post war cloning. Perhaps what allowed Sara/Mao to control the AFOS/PC flying rocks was a genetic key, likely something the PC could have used to ensure not just anyone could run aorund & pilot their high end bio-tech AFOS like super mecha, but for whateve rreason, perhaps cloning it, or implanting it artificially causes Sheryl's illness.
Cosmo nature indeed. The new wildcard here is that picture being taken in November 2047. The events with the Ginga Kujira happened in Spring 2047 according to the compendium. And yes, I'm still trying to tie that in with things, it could very well be that the completion of the GK/Zolan leftover PC test is what initiated the release of the Vajra in the universe. Both the Vajra & GK have something to do with a biologically bred folding ability. I don't know, but that all seems a bit too coincidental.