I have just lost the long story I wrote as an update, because I was trying to attached a picture that was too large :-((( In brief, I followed your advice, did some research and called Sunrise Sanctuary, a no-kill shelter, who came right away to pick Big Bird up! She barely protested it and did not make any attempts to escape from the back of the van while the ladies were loading up a few other things.

She is now enjoying her new home and swimming with Canada geese and ducks. I had observed her in the morning crawl into the lake in an awkward way, at least compared to the geese, but the ladies from the sanctuary, who saw her take a few steps, thought her gait was good. They have close relationships with area vets if she needs care, and they will try to learn more about her, such as whether she is young or old, pinioned or not, and whether she would be ok long-term, without her own kind. Her new home is a 16-acre property and is fenced to keep predators away, but she is roaming free inside (in an area smaller than 16 acres, I imagine), and, were she able to fly, she could do so at any time.

I'm sure Big Bird is at a great place and I will be going to visit her this week-end. Thanks so much for your guidance!!