You are not rushing things. With her respiratory numbers she is at high risk of severe respiratory distress or arrest if she catches a cold, seasonal respiratory flu (which flu shots don't prevent) or H1N1, the severe influenza that flu shots do prevent.
Your mother needs to be included in any discussion and the discussion needs to be ongoing to be certain that her wishes are her current ones.
Living Wills are legal and let family and doctors know the persons preferences but if any sibling chooses to object to the terms of her Living Will, he or she can delay or prevent it being adhered to if he or she pushes the issue. Doctors know that deceased people don't sue, but any family member can!
Having your mom assign Medical Power of Attorney gives that person the same legal standing in making medical decisions as your Mom would have if she could communicate. (It only applies if she is completely unable to communicate for herself or incompetent.) Medical Power of Attorney is a binding legal document. It is a difficult role for a loved one, but in situations where the family is likely to disagree, it is the one way in which her wishes can be enforced even if someone disagrees. It is extremely important to note that, unlike a Living Will, Medical Power of Attorney allows more flexibility for the Power of Attorney agent to consider the immediate situation, not just a blanket directive given. For example, if treatment or procedure wasn't desired by the patient but the situation turns out to be one not envisioned by the patient, or new advances have made the treatment less undesirable (better outcome, better quality of life, more affordable, etc.) or the family situation has changed, the agent can consider these factors and decide based on their understanding of the patient's general views. This puts the decision making in to "real time”, not past ideas and level of understanding. Ongoing communication, trust, and the strength to carry out the patient's wishes even if disagreed with are essential for the agent.
If the person assigned MPOA decides not to honor the wishes, they cannot be sued or legally forced to comply. The Medical Power of Attorney can be revoked by the patient as long as he or she can communicate. State laws, forms and details vary so look up the Medical Power of Attorney for your state.