I've made a post in my LJ regarding winged fics. What I have of winged Buffy there is:
Wings of an Angel by Ariadne (doesn't sound like it)
But the second is:
The Shadows that keep you safe by Areanna Whitewolf (WIP)
Takes place between Wreaked and Smashed and is seriously AU. Spike finds out that Buffy has been cutting herself and does something about it. Warning! AN: This deals with cutting and depression. Don't read if you can't stand that. Ditto to Xander being a bad one here.
Is that the one? Otherwise I don't know what it could be.