Sorry for the delay in providing an update, but it seems that much of what was presenting as my sister's rapid decline was an infection called C. Diff. When I got there, she had been in the hospital for at least 24 hours where they diagnosed the infection and began a treatment of antibiotics. She began to respond, and she has been home almost a week now, alert and lucid. There is even some talk about soon removing the tracheotomy tube she has had since the beginning of the year to assist her with her breathing.
She still has COPD; that has not gone away, and barring a miraculous intervention from God, it will be what she eventually passes away from. However, it is not as imminent as we first thought.
Thanks to all for your prayers. It was and is much appreciated!