Thank you for all your responses.
Yes she is very pretty, and very big! I am amazed that no one claimed her!
She is wearing a band, but we haven't attempted to read it yet. Maybe we can trace it? This should tell me her age, wouldn't it? The humane society listed her as a one year old bird, but they said it was a guesstimate by their vet tech. Here is a pic I took last night, she isn't as yellow as the pic shows, because it was under indoor lighting. Her colour is more greyed down than the pic shows.
I managed to read the band. I don't know what the order of the letters/numbers should be, but one number is sideways and it is 11, the other numbers are upright like the letters, and there is 09, and 20. I don't know which of these would be the hatch year? So I am assuming she was either hatched in 2009 or 2011, depending on whether the sideways number or the upright number is the year?
I am really pleased we adopted her! I managed to trace her band, and now have the breeders' name. An email has been forwarded to her from the bird club and I am awaiting a response. The bird is in fact only a year old, and I should be able to find out if she was a hand fed chick or not, and her parentage. She is indeed gorgeous!