She is having so much trouble getting air into those lungs that she's afraid when you hold her she won't be able to breathe at all, so she bites in her panic. that is my take on why she is doing this. I am sorry but I don't think you will be bringing her home either. Let her go with love and end her suffering. I am so very sorry she wasn't able to fight back, but her body looks like its had enough of this fight. (((hugs)))