It difficult to say, maybe another member will be able to give more insight on the matter :( sorry for your loss- must have been an awful experience but hopefully the other little guys are helping to cheer you up! Have fun being a chicken mommy! And
I don't know but this link might help it has pics too for comparison! http://www.tillysnest.com/2012/12/reasons-for-missing-feathers-in.html
All the best to your girl!
Aan poor little thing! What happens when you remove one of the bullies? Does the one left still pick on the little guy? Try and watch to see who the main culprit is and separate him/her from the other two otherwise the Wyandotte will remain the outsider. Good luck!