This very well could be end of life, but unless the bird is examined, there are no guarantees. Wildlife will separate themselves from other members if something is wrong to prevent predators from following sick members or to prevent the spread of disease. In your description, it could mean that she is starving, suffering from dehydration or exposure. It may be too late, but if you can capture her and get her to a veterinarian, you might be able to save her. Starvation, dehydration, infections, poisons and injury can manifest themselves in this seemingly neurological compromised behavior. The Regal Swan