Have Cat Questions? Ask a Cat Vet Online.
I am sorry that you have been waiting for a response. I recently just logged onto the site and noted that your question hasn't yet been answered. I am a licensed veterinarian with over 25 years’ experience and would be happy work with you if you are still needing assistance.
I can certainly understand your feelings on not wanting her final days to be stressful or traumatic, but unfortunately the agent that you are seeking does not exist. I am sorry to tell you that there is no orally administered drug that can be considered to be predictably effective or humane, especially with a cat in her state where her GI absorption and circulation are probably compromised.
Short of letting nature take it's course, your only other real option is to contact a veterinarian who will make a house call for euthanasia. Many veterinarians will as we all understand the situation and have all been through it ourselves. Good luck with your girl and I hope her remaining time with you is peaceful.
I hope this is helpful. Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please reply so I can clarify for you.