Sorry she isn't doing well.
That tissue doesn't look necrotic to me, but it isn't healthy. It is prolapsed tissue. I would likely guess she got a bad bacterial infection. She was pretty badly scabbed up that, I wouldn't be surprised if she got sepsis and it spread to the rest of her body.
Did you ever order the antibiotic I listed previously? If not, then it would probably be too late at this point. But that would have been the last thing I would have done, while tube feeding to keep her alive to see if they helped. Without that stuff, culling may be the best option, because she won't last long without drinking and eating. It is also very possible something else could be going on.