I'm looking for the name of a particular children's book. Gwynna??

I think the name had Gw in the beginning, maybe Q? Something like Gwenna? Or longer?

It's the story of a long-haired girl in a forest who's growing wings like an owl, and the tree gives her it's moss (which becomes a GORGEOUS green dress), I think she talks with other animals in the story as well...... beautiful illustrations..... Is this ringing any bells for anyone?