I believe from the records and documents I have read and deciphered, that Sanguinas was never recovered from Horus's battle barge...rather not fully. The reason why that happened is because they didn't have the resources or money to actually complete that action fully, most of their time and resources were spent fighting the Emperor. You also must remember that the time they found the body of Sanguinas, it was beaten and bloodied. Plus the fact that they had Illegal workers doing the job added the decrease in quality of executing the entire thing.
After Horus....or perhaps a more patriarchal figure slayed Sanguinas....some thing occurred most...suspect. By the time Dorn arrived to recover the fragmented body of his father and of Sanguinas, they later noticed under autopsy that Sanguinas was missing nearly all of his genetic stem cells, as well as nearly all his organs and varying cerebral corti. The reason why Sanguinas missed most of his genetic material along with his organs was because not because chaos wanted to create some super human leader, it was because they could sell high in the black market. I mean, chaos lords or other humanoids would pay huge amounts for even the liver of a primarch. This wan't anything about making a super human, but purely for cash and personal wealth.
In a lab else where...fueled by the genius of chaos, the direct genetic code of Sanguinas was manipulated...and a most "dark" and peculiar entity was fashioned in genetic facilities most concealed.... Ok, so I followed up on your sources and you are taking this completely out of context. Fist off, the dark and peculiar entity was actually chaos lord Melella and the operation was placing some, if not most, of the stolen parts into his wounded body. Again, read what I commented above.
She is called the Sanguine Mistress, and is an entity which is the result of genetic crafting directly of Sanguinas genetic code. Again, you misread your sources and took them out of context. This Mistress you are talking about was actually the corrupted scholar Emily Bergoph. The reason why she was mentioned was that it was her who sold the parts to Melella and also she preformed part of the operation.
With but a whisper she lulls to her side the masses, with but a wave of her pale ghostly skinned hand, reality warps to her whim....even now she further amasses her forces....controlled not by chaos, nor by man, yet wields both to her every desire. This is waaaaayyyy out of context of what you sourced this from. Emily, before the operation and before she sold the parts, held a private auction for this part. The auction ended up turning to a bloodlusted mess and finally resolved when Melella's men turned up victorious. Also her word during the auction had full sway as you mentioned because she owned the organs and the mass wanted them.
She must be stopped....for even now the Blood angels listen to her dark beckoning...her captivating wail has already begun to increasingly change the blood angels to their true form....following suit of her own dark visage.... Wow, this is totally made up. The blood angles fear her not because she some super human, but because she has the resources and muscle to launch a serious attack against the Blood Angels, because as she personally stated, she kinda has a vendetta against them.
Some call it the black rage, she calls it normality. I call that bullshit