It’s a children’s book (I believe) with beautiful illustrations. The story centers on a girl, very possibly with blond hair. She is kind to the animals and to nature, unlike those around her (perhaps she has a sister who is deliberately unkind). As a result, toward the end, the birds come together and make her a beautiful dress made entirely of brightly-colored feathers. The dress has a long train and peacock feathers seem to feature prominently. It might be a wedding dress.

I read it in the 1980s as a young child, but it could be an older book.